When I was a college student summer electrician, I discovered that most household circuits, at least then, were 15 amps, meaning that number 14 wire is used on a circuit that will trip at a continuous 75% of the rating (12 amps). A 20 amp circuit uses number 12 wire, and trips at (75% of 20) 15 amps. This is for all the outlets on that circuit, combined. Kitchen, bathroom, garage, and outdoor circuits are 20 amp. The electrical code may have changed, but your wiring is better than what used to be the norm. The actual outlets are different, but not for the fitment of the plug. You apparently used one that had not worn, from disuse. Absolutely nothing different can happen from using a 20 instead of a 15, except it will take more stuff to trip the breaker, including when you put a bobby pin into the outlet in an attempt to electrocute yourself.
I use a 30 amp, 10 gauge wire, dedicated circuit, because it was how I had wired my washer, and my electronics are now in the ex-laundry room. I did not want any power surges to ever get in the way of the sound. My two dual mono amps can put out as much as 1600 watts rms, full frequency (at 2 ohms), and I think it makes a difference. Of course, placebos can be wonderful.
