Over loading?

I've got news for you. It is not just the breaker. 20 Amp services have larger diameter (smaller gauge) wire to support the additional current draw. Changing the breaker and not the wire is theoretically asking for a fire. Most amps in home situations are going to do fine on a 15 Amp service. You can't drive an amp at full continuous power. It will be distorting on peaks and will sound stressed long before you get there. Just 3 dB down is 1/2 power and you are probably still distorting peaks at this level. This is why power is so important. To avoid clipping peaks and sounding stressed your loudest listening level should be 1/10th peak power or if you like listening at an average power of 50 watts, you need an amplifier capable of 500 watt peaks. Depending on the efficiency of the loudspeakers most of us are only listening at an average power of 1 to 25 watts. The outlier here is class A amplifiers. They draw a lot more idling than other designs unless they have a bias adjusting scheme.