Older fridges had to be 'dead-on level' in order for them to operate correctly. What most folks don't know is that there are a number of smaller tubes with-in the outer tubes that you see from the back of the units, and the ammonia/hydrogen mix depends on gravity to operate properly. The orientation of these inner tubes must be precise (as determined by a level fridge) to work as designed.
Newer units can operate in an RV that is 'comfortable to walk in' as stated by the manufacturers. Unfortunately, 15* does not qualify for this either
Do your fridge a favor and don't light it up unless it's 'level'.