If you can get hold of a clamp-on amp-meter and take a reading, it should show wether the current is high, there is usually certainly enough iron mass that sufficient inductance should not be a problem, there are others here that have used micro-wave transformers without indicating they had a heat problem.
I have seen articles though that some have removed the welded magnetic shunts on the side of the core as this apparently reduces the heating effect.
Al
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.