I agree with everyone in this post. I dont know what appliance there is that might be damaged by 20 amp service. In mostsituation a 20 amp circuit is preffered, especially in a place where you may have high amp appliances like microwaves ao anything with electric heating elements. It si ok to step down the breaker to 15 amps, but you may hvae a situation where it constantly trips. Most older homes were all wired with 20 amp circuits that were long runs and more outlets on a circuit than what is common now. That creates the potential for a heavy load on the circuit.With 12 awg wire a 20 amp breaker is more than adequate protection. Most modern wiring is 14 guage wire on 15 amp breakers with smaller loads and designed to be even more of an over protected circuit. Check to see how many outlets are on the circuit you want to step down and what devices are normally used on them.