The frying is only meant to melt the cheese and make the bread coating crisp. There is really nothing to “cook” because all the ingredients are already ready to eat. So, don’t fry the balls for too long. Don’t think that it is safer to cook longer at a low temperature rather than risk burning the bread crumbs with a too high temperature. That’s why it is important to test the oil first before dropping in the cheese stuffed balls. The quick frying is essential so that the mashed potato’s texture stays light and fluffy. If fried for too long, the potato will soak up too much oil. Worse, the mozzarella might start oozing out of the mashed potato.