I think the most important thing to remember is for your son to be able to speak freely and honestly with his coach. This is especially true for pitchers. That is hard for a 15 yr old esp if he is taught to really respect adults.
One thing I would caution you on is relying on any source for how many pitches a kid should throw. It is based on averages and your son may or may not be average. At 6-1 and 180 he certainly isn’t average size wise.
Another consideration is how much does he throw during the week and what kind of condition he is in. I know my son can throw ~80 pitches and be ready to throw again in about 3 days. He is also conditioned to throw that many and routinely throws 40-50 every day or every other day at the least. He has thrown ~65 one day and then another 40-50 the next. He is 15 and 5’ 11 and 140 lbs.
He seems to be blessed with a rubber arm, but I have spoken to his HS coach as well as other coaches some of whom have no vested interest in how much or little he throws and they all say the same thing see how he feels make sure he gets his bullpens in and make sure he is honest with his coaches on how he feels. His arm will tell him how much is too much. I wouldn’t recommend that for someone who pitches once a week.
He has never had an arm problem. A few times he has said he was kind of sore after throwing 85 pitches so he only lightly throws for a couple days and is ready to go. A lot of it is what you are conditioned for. Both his coaches and I keep a close eye on him and essentially drive him crazy with asking about how his arm feels.
One additional concern I would have is a 14 1/2 yr old playing with 17 yr olds and does he have the velocity to compete at that level (80-85 mph) and does he have the reflexes to protect himself on a come backer.