Have you also tried lowering the frame limiter of osu!? Using unlimited sometimes isn't the best choice.Yeah i'm playing fullscreen, tried locking fps to 240 and at least now it doesn't seem to give me random frame drops, but still i feel like i should be able to get way more fps...
Also, play in fullscreen and not windowed mode, as that may give you additional lags.
I've had this exact problem before. It solely deals with the capabilities of the laptop. Osu isn't a particularly tasking program to run but it can still lag of course. If closing all unused applications doesn't reduce the lag then the only other thing I can really think of is dedicating more of your memory to ram.closing all other apps doesn't have any effect, i have 8gb of ram though, it should be more than enough to get way more fps than this, no?
For example, my sister's laptop is a lot weaker than mine and she only gets ~1.5ms. Though her laptop has an amd graphics card, so I think the problem has something to do with nvidia.