It looks like you have a huge amount of instances for heavy geometry, like bushes and trees. So the USD may only show up at 500mb, but it could be much much bigger on export. I don’t think it’s about deleting more but finding out what in the scene is causing a hang. There may be just one element or one group of elements. First of all what format are you trying to export to ? Second, does an export of any file cause a crash, or is it specifically this file ?
Do you have any special elements in it like paint objects ? Try to delete very heavy elements first.
If you want to “collect” your file and zip it up, and send it over that would be great.
I made rough placeholder objects for the most complex ones in Composer. This way I got the city scene much more lightweight and exporting to USD / OBJ / FBX works ok.