TheShy Yes this is as expected as if you will pick full geometry RN will import original full geometry into the file as embedded blocks that's why the file is so big. If you will import proxy then the proxy mesh is imported only and the original mesh stays "detached" from the file as the proxy is only "link" to an external asset.
Here is also an explanation of why RN does not delete those imported and why you should use _Purge in such a situation. If you would import something else not via RN and put it as an entity and then delete entity RN would delete this block also which may not be expected by the user. It could delete something in your design, which would be far more irritating than a bigger file size.
TheShy delete the Blocks in Rhino, and save 10MB (I only have a rectangular plane at this time)
TheShy clear unused blocks can reduce the file size to 12MB
Maybe those are textures saved in a file? Since v7 Rhino tends to save textures within the 3dm file. Check what will happen if you'll save it using _SaveAs and uncheck save textures.