DPElite,
Sorry to hear about your son. Be sure to let us know what the results of the MRI w/ Dye were and if surgery was needed. My son who is also 15 just had his TJ surgery on the 23rd of December. His innings were monitored closely as well but still tore up his UCL. While not as big as your son he is still good sized for 15 (6" 2" and 190lbs) and threw hard. After the fact the physical therapist found that his shoulder was extremely weak and likely was a culprit in the elbow blowing out. The weak shoulder led to his dropping his elbow due to tiredness which put strain on the elbow. Couple that with him having a 7mph jump from the prior year (1st winter working with a pitching coach really helped plus a couple inch growth spurt)and throwing with max effort too often it isn't surprising that his still immature arm couldn't handle the stress and blew out. UCL tears aren't just from overuse. sounds like your son's injury is more along the same as my sons. I hope it all works out for the best but if it a torn UCL and TJ surgery is required at least they are young enough to bounce back in time for their all important junior year and summer of junior year recruiting wise.
Good luck and keep us posted!!