If you didn't trip the breaker it was not the limiting factor. However, the wire gauges will be smaller on the 15A circuit (Or higher? I still can't figure out AWG. LESS COPPER!) and thus, voltage sag will act like a compressor on your signal in the earliest stage of your equipment chain possible. The smaller the wire, the more voltage sag you'll get. When I turn up my clone amp in my house in France it dims the lights. When I do so in my house in Germany, no voltage sag occurs. Maximum sustained power output of the amp is around 4KW for several seconds. 3KW long term. I saw the amp draw over 15A from the wall on the 230V circuit. Skhorn in a 3000cuft room. Loud!
I'll be using 30m (100ft) of 8AWG speaker cable for heavy duty sub testing to mitigate cable losses (with the amp on a 230V 32A circuit).