SMB is notoriously slow over a VPN, what speeds are you seeing? I've done a lot of file corruption using SMB over a slow link, it doesn't resume well and often thinks will look fine when they're not.
You'd be better off sharing a Google Drive, or something similar, on the two devices.
There's also rsync, it's worth checking out.
Search for "fastest cloud drive" and compare the speeds in the reviews with your speed.