My grown son is in an IOP currently too.
I must say I am so Impressed that your son is 15 and You are doing something about his issues. Doing and actively involved and educating yourself. I am sad that I could not face facts when my son was a teenager. I used the lines like: All kids smoke weed, Oh he is not like his friends, they just have fun and will grow out of it.
My son was busted at 18 for scales and weed by a St Trooper. The trooper called me at midnight to come down the street and get my son. Trooper said the young man wants help, please get it ....I thought I did the best, but the counseling was not the best. Fast forward to 24 years old, he brought a "girlfriend" who was a Heroin dealer into my home. The local police watched my lovely home as they wanted her. I left my home one morning and got pulled over by two cruisers one block from my home. I got explained to what was going down, that they were waiting for two County police to come and it was best if I let them in. They surrounded my home as I sat in the porch swing. I will never let that memory slip from my mind, MORTIFIED, embarrassed, angry and so much more. They did not take my son had no interest in him, but the lady who had the stuff and three warrants.
One Officer took me aside and said "DO something NOW! Get him out of the area he is a nice guy, just connects with bad people". Then the words that are carved in my mind, he said, Your son will be in prison with in two years and dead within 4.
Again I tried to get him help as best I knew how, I sat through the withdraws. Moved him to a great job at his father's work one state away. My son just could not stay away from the trash. With in 13 months of that incident, he was in court for something...mommy paid the fine to keep him out of jail. Within 25 months he was in ICU on heart monitor waiting to recover or die.
That office hit the nail on the head that day.
Do as much as you can for your son while he is still young, you seem so strong.