My personal opinion/experience: As long as you feel comfortable sleeping in your camper, you should be fine.
The manual for your refrigerator will give more information. I googled and randomly came up with this quote from the manual for their NX6/8 models:
"The refrigerator is made to operate within 3ยฐ off level side-to-side and 6ยฐ off level front-to-back (as looking at the front of the refrigerator). Operating it at more than these limits can cause damage to the cooling system and create a risk of personal injury or property damage. Make sure the vehicle is level before you operate the refrigerator".
We use the built in level in our smartphone for leveling, btw.
Additional info: The cooler unit in the back with the sloped piping needs to be fairly level looking from the refrigerator door to keep the gravity flow running. In the other direction, it is more tolerant (looking from the refrigerator side). The way most fridges are installed that means the vehicle needs to be fairly level front to back, more so than side to side.
If parked for a short while, for shopping etc., it doesn't really matter. Over night, I am less tolerant than my frigde. So is the shower drain.
2014 Ford F350 XLT 6.2 SCLB + 2017 Northstar Arrow