Need Help w/ Fuse Panel Rating

[thedink9]

I'm now getting around to replacing all my breaker switches and noticed the oll breakers were all either 15 or 20 amp.

This seems too high for most of my applications which include: bilge pump, washdown pump, electronics, dash panel lights & compass , 2 - rear deck spot lights, 1 front spot light,and Nav. lights.
Can anyone give me the formula in helping determine what correct rated fuses to use? Dink