How to change the cache configuration of uploading?

This is true - the default 8M chunk size is a larger problem the more bandwidth you are trying to use.
I would still recommend at least 32M in your case though, or 64M just tp optimize throughput.

Note that this only affects uploads - and only when using a Gdrive remote (so if you are running it via the webdav then it is the VPS's Gdrive remote that should have this setting changed - while if you run it via VPN from home then it should be enabled in the Gdrive remote at home).

I think you should be able to see a clear difference even on your connection - but probably not a huge difference.

PS: Due to high loads right now (due to Corona) on Google and many other cloud providers, the transfer rates are very unstable right now. It is not an ideal time to make exact speed-tests because performance seems to fluctuate: