Three degrees is a surprising amount off level; it's about five inches difference side-to-side (assuming an 8 foot wide RV). That's far, far more than a quarter bubble on any level I've seen. (I don't think the bubble sizes or markings on levels are particularly standardized, either, though I may be wrong there.)
Basically, if the coffee in your cup isn't all slopey, and the eggs in a frypan don't wander to one edge, and the shower drains properly, you're more than level enough for the fridge to be happy. On the other hand, if it's obvious you're slanty where you've parked, then turn the fridge off.
I tend to level my RV far more precisely than is really needed for the fridge because I like to be level.