Don't put a 30 amp breaker in a 15 amp circut !! that is a fire waiting to happen. For a 30 amp breaker you need 10 gage wire. If you wire is less then 10 gage the wire burn up before the breaker ever trips. Get a new 15 amp breaker and try your tests again.
It is an intersting expermint though, After you replace it with the correct size, run it for a few weeks and see what happens, Then switch it back and see what difference you hear.
Mark