Hi Wendy, my name is ***** ***** will assist with your query today.
The tilt is to assist with moisture in the fridge to run down the wall and out to the evaporator.
In some models this slant is built into the internal wall, with this model is design its by external design.
That said a 6mm delta is significant, and would have expected it to be more 2-3mm, certainly not enough for the door to want to swing shut when open.
Are you sure the floor is level?
I would say 4-5mm is at the the tolerance I would accept, however if its causing the door to keep closing your best option is to return it.