A 1.5 hp submersible pump motor will draw any where from 10 to 12amps.
If your pump is popping the reset, it's drawing more than 15amps. Most 1.5 hp resets are around 15amps. I would try a new capacitor.
Sometimes even on new boxes, the capacitor can have a bad connection on the top where the wires connect.
Its cheap and easy to change. Look at the cap where the wires attach, see if it look a little burned.
Do not touch the tabs on the cap!!! If it is good, it will have a high voltage charge.
If you have a cut wire, it should pop the reset every time it tries to start.