LIVE: Memory spikes when importing a json with a large amount of sprites

While importing a json file with a large amount of sprites, memory usage spikes. The test asset uses a 2000x128 texture with 1024 elements.

1. Launch: UE4Editor.exe
2. Open the user's Spartan_Saga_New project
3. Import the user's demo spritesheet.json

Result:
The import process will take over 8 minutes, during which time the engine will increase its memory usage to roughly 28G.

Extremely low performance on importing or changing assets in Paper2d