It's because you had 10 players rostered for the game.
Something is wrong with the lineup like that, if you're training 2 players in a game you should have 8 players rostered if you want your trainees to get 48 min
My recommendation
PG
1.Trainee 2. trainee 3. trainee
SG
1. trainee 2. trainee 3. trainee
SF
1. starter 2.backup SF 3. backup SF
PF
1. starter 2. backup pf 3. backup pf
C
1.starter 2. backup c 3. backup c
Like you said you had strictly follow depth chart, which is a must for 48 min, you also want to select let them play so they dont get taken out in foul trouble.
Also if I can make a recommendation, for training the best tactics are slowest paced tactics (patient, princeton, and low post)
On the Defensive end you're going to want to play 3-2 or 1-3-1 zone.
All of these tactics are meant to slow the game down decreasing chances of a player fouling out.