Have you tried making the game resolution lower?
Try switching to a lower one, see if this helps
Have you recently changed anything in the nvdia control panel?
Try changing it to quality or balanced mode
I still don't think the lag happens because of a lack in resources, something must be in conflict in your gameplay
Try installing osu! In another location and see if the lag is gone
Also, try temporarily disabling your tablet drivers if they might be the cause of the lag
Update your directx, sometimes the cause of common errors.
Try running osu with the GPU or without, (right click osu, "Run with graphics processor")
If you have any power usage program that modifies how much performance is used make sure it is enough for osu! To run correctly