Saving/Loading Large arrays in runtime, large lag problems (C#)

I have been toying around with my voxel terrain generation and because the game i am planning to create is a city simulator and will have multiplayer so will require large scale maps, i wanted to add chunk loading to the game so everyone who joined a game didnt have to load every single chunk, when i do save or load these pieces of voxel terrain, it laggs for about 10 seconds before running perfectly again

This is what it looks like
...

Saving/Loading Large arrays in runtime, large lag problems (C#)