The lag spikes and a missing ceiling

[Cranky Old Man]

You dont know much about that stuff, since you would instantly see two things you said that dont work together:

not much RAM

and the game loading in textures MID-GAME

Do you know what texture streaming is? Its the mos advanced technique out there that is supposed to keep memory clean and stop game from lagging. But its bound to a PC that actually has the min req RAM.
So if you dont have 8 gb of ram delete your thread, cause thats the min req of the game. Anything else is your problem.

I only have 6 GB, but the game works fine AFTER all textures have been loaded in, which makes me question the minimum requirements. I guess the game tries to load all textures at load time, then fails, and then loads the game "without" textures, but then streams it back in. ...so why can't it, at load time, begin loading the textures that the player can see, and then the textures local to it, and then the textures furthest away? ...and settle for the textures that it managed to load in? That would make the game run on a 6 GB machine or lower.

Also, a missing ceiling bit is still a missing ceiling bit.