First, just moving into a professional program and not being a student can have a guy put on 10 pounds of muscle in an offseason, usually while shedding some fat though. If the program is specifically aimed adding 15 net pounds though, for a guy his size its probably not hard at all. When you have the resources to streamline the dietary habits and the lifting 15 pounds is nothing. I weigh in at a hardy 215 and workout modestly nowdays, but I could easily swap 15 muscle for fat or just tack on 15 in muscle if I made it a mission (and I'm 50+).