Breakers work by sensing heat I think(?) through resistance. Household breakers seem to trip at various rates by brand. My guess is if a 150 amp fuse blows(regardless of rate), a 120 amp breaker wouldn't stay closed for more heat than the 150 amp fuse, but who knows? The breaker could delay just long enough to work for your situation. How often does the fuse blow now? I have an old 150 amp breaker for my ideal windlass and it's never tripped yet.