$FCMemoryAvailable is a global variable which is set to an integer n, where n is the available amount of main memory in MB. The default is 1/4 of $SystemMemory. It should be increased if possible. The higher $FCMemoryAvailable can be, the more intermediate steps do not have to be repeated by FeynCalc.
Overview, MemSet, FCMemoryAvailable.
$SystemMemory32898408448
Floor[$SystemMemory/10^6/4]8224
$FCMemoryAvailable8224