Which LED do you seen turn red? Below is the LED guide for an IAP135. Are you able to attached a console cable to the AP and post the output?
Try also plugging the IAP315 into a standalone network (so it is separate from the 215) and see if the AP boots up. You may need to upgrade the IAP315 to 6.5.3.1 then plug it back into the IAP215 network.