ATP is ATP... I've heard horror stories from that place, and I've also met an instructor or two from there who were just fine. I think the problem lies in the fact that they churn out pilots at such a rapid pace that it can become difficult to identify/rectify problems in some cases... and those cases get pushed right through the door into the aviation world regardless. I would recommend somewhere you can build more multi time than just 15 hours though. You will need it. Especially at your age if you are hoping to get to a regional airline.