I think you may have discovered the "average file size" for your system. The simpler the mesh, the smaller the file. Ways of reducing the file would be to inspect for duplicate faces, edges and so forth and to delete these where not needed. Use xray mode to check for internals. The greater the "physical" distance from 0,0,0 the more likely you will have navigation problems resulting in delays. Also colors/materials/textures have an influence on the file. Where repetitive identical geometry occurs, these could all be instances of one component rather than separate components.
I think you can help reduce the layers by exploding then renaming the components one by one. Then look in Top Menu: Window> Model Info> Statistics, Button: purge unused, and optionally button: fix problems. You may have to specify the components to be on Layer0, I am not sure. I am not as practiced with layer usage.
There may be simpler ways of doing what I suggested. This is just how I would do it given my knowledge level. There may even be scripts/plugins for some of these operations.
