The heap on windows is single threaded causing it to lag behind linux in performance in allocation heavy multithreaded scenarios, BVH building is a prime example.
See https://developer.blender.org/D6218 for benchmark results
for testing with the allocator enabled/disabled you can set the environment variable TBB_MALLOC_DISABLE_REPLACEMENT=1 to disable the TBB allocator.
Reviewed By: @sergey
Differential Revision: https://developer.blender.org/D6218
d60a60f0cb