MLB Prospect Debuts: Fantasy Baseball Waiver Wire Pickups and Rookie Stashes (Week 15)

Mike's fantasy baseball prospect stashes, sleepers, and rookie waiver wire pickups for Week 15 of 2025 -- recent MLB prospect debuts and potential call-ups to monitor.

Summer is racing by us, and with that, major league teams are starting to promote prospects to their rosters.

The following are a few players who should generate interest among fantasy baseball players.  Some look like they will get full-blown chances, while others will eke out scant playing time and a few at-bats to try and prove they belong at the game's highest level. As we near the trade deadline in about three weeks, look for prospects to get the call, and with that, look for opportunities to improve your fantasy rosters.

These players offer intriguing upside for the fantasy manager willing to show patience with rostering a young player, as opposed to rostering a boring veteran who may not help your team at all. Let's take a look at a few players who intrigue fantasy players.

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Fantasy Baseball Hitter Prospects To Target

Colson Montgomery, SS, Chicago White Sox

Level: Called Up

2025 Stats: 17 PA, .385/.500/.538, 1 R, 0 HR, 2 RBI, 0 SB, 17.6% BB%, 17.6% K%, 195 wRC+

Montgomery was long thought to be the White Sox's top prospect, but there has been some dimming of his star over the last couple of seasons. This was largely due to injury and some mechanical issues he was having with his swing. Last month, the organization sent him to its Arizona complex to work with guru Ryan Fuller on reengineering his swing.

What separates Montgomery from other hitter prospects is the sheer power and speed of his swing. See his Statcast info below on his average bat speed thus far with the White Sox. Montgomery generates an average bat speed of 76.7 MPH, which is five ticks faster than the major league average.

Manager Will Venable has started Montgomery at shortstop every game since his recall, hitting him seventh more than any other spot. This should be a good spot for Montgomery to adapt to the major league game. I expect a higher-than-average strikeout rate with a potential for big power.

The Sox want to give him some runway playing shortstop, and in the process, will move another top prospect, Chase Meidroth, back to his natural position of second base. Figure the Sox, with nothing much to play for other than to give rookies time, let Montgomery play every day at shortstop.

Tristin English, INF/OF, Arizona Diamondbacks 

 Level: Called Up

2025 Stats: 272 PA, .336/.387/.563, 41 R, 11 HR, 43 RBI, 0 SB, 7% BB%, 14.2% K%, 125 wRC+

English was recalled last week in a flurry of moves that saw Pavin Smith go to the IL and Tim Tawa optioned back to Triple-A. At 28, it would seem that English is past prospect status, but this is a guy who could be a useful piece to a struggling Arizona team.

English can hit; his .336 batting average was among minor league leaders. He is not a big home run hitter (career-high is 24, and he has 11 this year) and doesn't steal bases. But his OBP in 2025 is .387, so he gets on base at a high clip.

English has experience playing the corners both in the infield and the outfield. Given Jake McCarthy's struggles to hit this season, English could see some playing time, as the only outfield fixtures are Corbin Carroll and Alek Thomas. It will be interesting to see if manager Torey Lovullo gives him a chance here.

Anthony Seigler, Milwaukee Brewers

Level: Triple-A

2025 Stats: 267PA, .277/.416/.465, 43 R, 7 HR, 35 RBI, 20 SB, 14.8% BB%, 19.1% K%, 142 wRC+ 

Seigler intrigues me; he was a first-round pick of the New York Yankees back in 2018 who never made it there. Yet, he fits the current mold of the player the Brewers and manager Pat Murphy seem to like: gets on base, limited power, can steal a base, and take a base on balls. See his minor league record below. He was hitting .277 with seven homers, 35 RBI, and 20 stolen bases in Triple-A when he got recalled last week.

The biggest obstacle for Seigler will be finding playing time on a roster that includes guys similar to him, like Caleb Durbin and Joey Ortiz. However, one path to playing time for him could be behind the plate, where William Contreras is dealing with a nagging finger injury. The current backup is Eric Haase, who is hitting .220 in 2025.

Fantasy Baseball Pitcher Prospects To Target

Shinnosuke Ogasawara, Washington Nationals

Level: Called Up

2025 Stats: 2.2IP, 13.50 ERA, 2.63 WHIP, 12.5% K%, 0.0% BB%, 7.58 FIP

Ogasawara is an interesting "prospect" signed from Japan in January 2025. Signed to a two-year contract by Washington, he did not make the team out of spring training. At 27, he got the call last week and debuted with just over two innings, allowing four runs and seven hits while striking out only two Boston Red Sox hitters. Given the paucity of Washington starters right now, he slots into the rotation and is slated to get the Milwaukee Brewers this weekend.

The lefty looks to be fairly typical of Japanese hurlers; he doesn't have much velocity but relies on great command, control, and guile. See below. I recognize it is a two-inning sample, but Ogasawara threw four of his pitches over 20% of the time and never topped out at more than 90 miles per hour. He is going to get by on inducing ground-ball outs, and his career-best strikeout percentage was 24% in 2022.

Cam Schlittler, New York Yankees

Level: Called Up

2025 Stats: 76.2 IP, 2.82 ERA, 1.21 WHIP, 31.9% K%, 8.4% BB%, 2.52 FIP

The first thing you notice about Schlittler, the Yankees' No. 5 prospect, is his imposing size; he is 6'6" and 230 pounds. He is primarily a fastball and curveball pitcher but has different variations of both pitches that he throws.

The curveball is of particular interest as Schlittler throws a bigger one that is the typical low-80s type to left-handed hitters, while he uses the cutter and the slider more often against right-handed hitters. The fastball is high 90s, and he tends to throw it at the top of the zone.

Look at the box below. Schlittler led the Yankees farm system in strikeouts last year with 154 in 120.2 innings. He also induces a high level of groundballs with his pitches. Given manager Aaron Boone's dearth of starting pitching options due to season-ending injuries to Gerrit Cole and Clarke Schmidt, Schlittler should get a long look this month in a starving rotation. If he does well enough, he could stick, and the Yankees could look to augment the team elsewhere at the trade deadline.

Jack Perkins, Athletics

Level: Called Up

2025 Stats: 9.1 IP, 1.93 ERA, 0.75 WHIP, 28.6% K%, 5.7% BB%, 2.98 FIP

Perkins was recalled with little fanfare, but he looks the part. What I like is that it would seem that he would be able to slip into a starting role should the Athletics lose a starter or decide to make a change in their rotation. Perkins has pitched in three games thus far, and he has saves in two of them, both multiple-inning saves. He could also fit at the back end of the bullpen should the organization sell off current closer Mason Miller to the highest bidder.

Perkins features a four-seamer and a sweeper/slider but also mixes in a cutter and a change-up. The four-seamer has good velocity at over 95 miles per hour (higher in relief than in starting), but the sweeper appears to be his true "out" pitch; he threw it over 40% of the time in his last outing on July 4th. Watch his usage in the coming weeks. It will be interesting to see how the team and manager Mark Kotsay use Perkins in the second half.

More Fantasy Baseball Prospects and Rookies