Checking the Blender version on the Kits a lot of the buildings have the same duplicated props multiple times (e.g. The Central Library from Neo NYC has the prop "Benches" 15 times inside 3 different objects, and considering "Benches" is composed of a solar panel roof and 2 benches to each side, the same bench model appears 30 times, also the oval-like chair appears 46 times inside 10 different objects). That can be reduced by creating "Linked Duplicates" from the prop inside Blender so the program knows it's the same mesh, reducing a lot of memory.

I checked Mission to Minerva too, and some of the medium size buildings are just the individual pieces joined together. By considering Linked Duplicates those buildings will not be considered as new and different objects and meshes, freeing memory, file size and making blender run faster.