All of a sudden I can't build lightning/building is extremely slow?

So I got UE4 a couple weeks ago and I’ve been experimenting. I’ve built a really small level for the FP Blueprint, really basic level. It’s just a rectangle room with a couple of lights. Everything was going fine, building was fast and then I downloaded some assets just to mess around and put them (the Berlin Apartment I think it’s called) on my level. So I use this window asset and put it on a wall and all of a sudden building is slower. I think maybe this is normal? So I put another 7 of these window assets and then try to build and it gets to 1% and always gives me this kind of error:

Error <None> === Lightmass crashed: ===
Fatal error: [File:D:\BuildFarm\buildmachine_++depot+UE4-Releases+4.7\Engine\Source\Programs\UnrealLightmass\Private\Lighting\LightingSystem.cpp] [Line: 1324]
Static lighting thread exception:
Fatal error: [File:D:\BuildFarm\buildmachine_++depot+UE4-Releases+4.7\Engine\Source\Runtime\Core\Private\GenericPlatform\GenericPlatformMemory.cpp] [Line: 54]
Ran out of memory allocating 267911424 bytes with alignment 0

I’ve tried restarting my laptop (I tought it ran out of virtual memory and maybe just releasing everything would fix it) but to no avail. Also tried building the regular FP Blueprint level it comes with and it was reallyyyy slow building it when before it was quite fast. I searched around and someone said I could put a Lightmass Volume Importance to work around this but it didn’t fix the problem. I don’t think I’ve changed any settings at all.

My machine is a Clevo W230ST with 16GB Ram, i7 CPU and a GTX 765M GPU. Thanks!