So I bought a 15 amp circuit breaker instead of a 20 amp CB online to replace the 20A CB that is not usable anymore.  This breaker will serve the lights, accessory plug, bilge, aerator pumps, and depthfinder.

Would I be ok with the 15 amp breaker or should I go through the trouble to exchange it.

Just depends on what you plug into the acc plug.  You are proabably pulling no more than 10 amps with lights on and everything going right now, but a 100W spot light with everything else going would probably trip the breaker.