A pitcher's in game fatigue is based on the pitch count when he starts the plate apearance. Thats why sparky lets him throw over. So, if you havea guy set to a 15 max, and starts a PA at 13 and finishes at 19, he was just fine. You can set it at 15 if you want without worry.
Also, one ofthe few good things about LIVE is the ability to see how fatigue works. Load up your team and put that guy in to pitch.