The ONLY way he will avoid a significant sentence (both for his probation violation and new charges) is to drop the dime big time.
We work on the 10 for 1 basis. If you've facing 15 years, you need to help us build cases that will result in sentences of 150 years.
As for what he's looking at, I doubt anyone here can give you a realistic estimate. It depends on previous history, location, who he's selling to, etc etc. Maybe 10 years, serve 5...?