Thats very dangerous because a device that draws 12.5 amps (1800watts) continuous will trip a 15 amp breaker if you put a 20amp breaker on that line you are causing a fire hazard if the device is only rated for 15amps and starts to over draw due to a problem as the breaker will not trip until it hits 18amps continuous. That is not code what so ever, VERY dangerous. 20amp circuits should only be used with devices that require 20 amps.hmm Every house i have ever built , all our electricians use 12/2 , with 20 amp breakers. It makes sense since lighting is pretty weak.. I think you can use up to 80 watts on a single 15 amp breaker,
But anyhow this is way off topic so we should start a new thread if we want to talk about this more.