Unable to show all levels for huge map

So I tried importing this huge 47x47 kilometer heightmap of some chinese mountains into unreal engine and I got 64 levels.
I tried loading all of the levels, but it only loaded some of them, and when I tried loading the rest of them, it only loaded a few, and unloaded some others. Is there a max size for levels? Is there any sort of workaround? Help would be appreciated.