I would suggest checking out the
MLB 15 Sliders Subforum on Operation Sports if you want to look specifically at sliders.
Another recommendation would be to download the OSFM (Operation Sports Full Minors) roster from the roster vault. That way if you are playing franchise mode, you can play with the real minor league prospects instead of fake minor leaguers. They update the OSFM roster throughout the year. Operation Sports also makes a Hybrid Roster, which means they edit the player ratings based on stats and a special algorithm they use. They put a lot of work into making those roster files, and it certainly adds to the realism of the game.