I believe you meant to say Phoenix 60 amp ESC and Mega 16-15-2 (not 6-15-2), otherwise known as the Mega 2-Turn. The Mega 2T can only handle up to a 3S pack...your 4S pack is way over the voltage limit and way under current (2200 is too small at 4S) as far as what it can maintain and that is causing the cutoff. Your ESC is seeing high current draws, well over 60 amps, causing it to cut out... with the 4S pack, the voltage probably dropped to half of the normal @15vdc as it cannot handle the high current draw. Another bad thing as your RPMS just dropped to half.

Get a 3S pack that is a 20C 3200 or 3700 Like the Kokam or Polyquest, or you can go with a Thunderpower 3S 4200 Pro Lite and get the 450+ watts that the motor will run and handle. Both you and your power plant will be much happier.

Carl