If you choose 15 alts, it is better to choose them from the top 100 markets, because if you look for coins that are in the middle of the market, you can get to the scam
Obviously, these are top 100 coins. They have less diffusivity and profit retention qualities. In my opinion, 15 coins might be considerd much but then if half of what he has picked give good returns, then he's fine. I wish him all the best of luck and may the turbulent cryptocurrency tide be gentle on his portfolio