I suspect its from the texture files which are 2048px. The files are used by all 4 assets. And I know there is a mod which recognizes duplicate texture files and only loads them once. So I hope in-game resource hit will be small if you use the mod. I think the mod is "Loading Screen Mod" - https://psteamcommunity.yuanyoumao.com/workshop/filedetails/discussion/667342976/1636416951459546732/

Very cool, but do you know where the huge file size is coming from? They're larger than whole buildings...

Is your geometry optimized? Are your textures 4k or something??