Guide: Condition loss and Ability gain in games

[Bog Igre]

I play with 2 teams for last two seasons and won the treble bouth seasons..But i always have a feeling my players will be beater if I play with 15 and not 22 players.I played with all young players and at the end of last season my 13 players were 7* players and the rest of them were 6* players so i couldn't sell my 6* players in order to have more weaker team for next season cup and CL draw and the resoult is +1 and +2 level cup and CL and my chances for third treble are very low.So I think the right way to play this game is to have 14 youngsters that will become 7* at the end of the season and 9 average players plus 2 young players from academy.And also if I figured out right young players develop with same speed if they play games or train with 4 level training drills???Am I right?