silly question: if you can't "tell" by listening then why bother obsessing about when it "leaves" class A? It's not like your speakers are suddenly fed a distored signal the magnitude of which swamps out low level signals-- 15 watts rms (in any class of operation) in a 20x15 room with your speakers would be quite loud.
forget all the numbers nonsense: does the combination sound good to you? I bet it sounds excellent!
forget all the numbers nonsense: does the combination sound good to you? I bet it sounds excellent!