How much space left you have on your c: drive? Maybe chia is using windows temp folder (usually your c:\windows\temp), and just choked that one? Kind of unlikely, but worth to check.
Also, could you check your g: drive, how big is right now v2 db? Is it there are all?
Lastly, instead of letting chia decide what are the paths / destinations, maybe you could do it explicitly - How should I upgrade Chia v1 DB with boot drive almost out of space? - #3 by Jacek
Just change there that %userprofile%… with g:\path\v1 and g:\path\v2. Maybe to not get chia confused just create another folder for v2.
Lastly, what is your g: drive? is that HD or SSD/NVMe? When I did sqlite vacuum before, it took me roughly 30 mins (on NVMe), so let say double that maybe to get how fast it should go. Of course a bit more for HD. Still, not 12 hours for 30%. With that speed you can just scratch your db, and sync from zero.