I have seen some highly rated P4 programs go into a season with less than 12 scholarship players. There is not a lot of great ways to play and pay 15 players. Many coaches like to keep at least one spot open all summer, just incase the right player comes along. Once you have a roster with what you need for a solid rotation and good backups, you only want to add someone who will elevate your program. Otherwise, go with what you have. 12, 13, 14, or 15 players? It's hard to have more than an 8 to 9 man rotation. The rest of the team is there in case of injury or to fill in as the scout team. With 15 players, it's a good bet that 5 won't see the floor.