When I put together my ranking of the top 100 prospects in baseball each winter (here's the complete guide to the prospects package), I base it on the overall potential I see from each player over the course of his first six years of service in the majors -- the length of time he'd spend with his parent club before reaching free agency -- and apply a discount to players who are further away from the majors. The prospects' potential production strictly in 2015 is only a minor consideration, because weighing it more heavily would lead to a list more populated with low-ceiling players rather than the potential All-Stars I think have more asset value.
To balance that out, I produced another list, this one ranking the top 20 prospects in baseball based solely on how much value I think they might produce in 2015. This list includes one of my least favorite kinds of forecasting (because I don't do it well and have no idea how to do it well): estimating playing time for the next seven months. So you're getting my best guesses -- guesses is the operative term here -- for probably 30 or 40 players underlying the rankings below and my decisions on which players to include. If a prospect you like isn't listed here, it might be only because I don't think he gets the playing time in 2015 to make the list.
I don't consider Boston outfielder Rusney Castillo or Arizona outfielder-maybe-third-baseman Yasmany Tomas as "prospects" due to their ages (27 and 24, respectively) and lengthy experience in Cuba's Serie Nacional, but were I to rank them, I'd have Castillo third on this list and Tomas sixth. I believe more in Castillo's athleticism and glove; Tomas is bigger and stronger, but he's not a great athlete and doesn't have Rusney's bat speed.
With that, let's look at the top impact prospects for 2015:
Bryant probably won't head north with the Cubs on April 5, but he'll be at Wrigley Field maybe two weeks later as the Cubs look to push off his eventual free agency by a year. He's my pick right now to win NL Rookie of the Year, likely to hit 20-plus homers and get on base at a strong clip even with a strikeout rate that will probably top 25 percent.
2. Jorge Soler, RF, Chicago Cubs
If Bryant doesn't win the ROY award, maybe his teammate will. Soler hit the majors like he was fusing deuterium and tritium nuclei, but it lasted only about a week before he discovered the travails of a hitter facing the major league strike zone.