Plz help. .stl file behaving choppy

Hello. I recently started using blender. Watched YouTube tutorisls
and am taking the Udemy course. I was sculpting a chess puece
in blender, and all the sudden it spazzed out and nothing would move
on screen. My pointer still moved, but everything else was lagging super hard.
i was using my 2012 MacBook Air. Which I know is not good enough for blender.
so yesterday I bought a new ibuypower 16gb /Nvidia thx 1760/ 1tb/256 ssd/ ddr2700.
I figured when I file shared from my Mac to the PC (win10) the file would work correctly.
its still the same, but moving very choppy. If I create new file, everything moves fine.
All my other files I transferred over still work fine. Only the one file will not respond smoothly.
i sculpt 3d for printing. I’m not doing animation or any crazy
stuff. Just chess piece modeling basically.
help plz.

Importing .stl file means you are importing a clean polygon object. (triagular faces at that).

First check in the upper right hand corner for the vertex/edge/poly count. If they are extremely high then it woudl be the reason for the slow down.

Additionally did you add subsuface division (or even by mistake like pressing CTRL+3 - or higher). That would definitely mess up the refresh of the scene. Check in the modifiers panel and see if the modifier is there and if it has anything above 2. if so, reduce it to 2 or lower (or delete it)

beyond that i’d have to look at the file itself (screenshots woudl be helpful to judge any furhter)

i don’t know how to check modifiers.
my v//e/f counts are high, since I have multiple objects.
I even deleted the highest count object, down to 3,000+ vertices but still can’t do small movements when I transfer, rotate, or scale.
It seems that when I select the object, and try to move it, its only moving in large increments (like 1 unit of measure at a time)
instead of smoothly.
when I return to a previously save file of it, its fine. But the current most recent will not work properly.
appreciate the help.
I need to save more often. Thats a day worths of sculpting difference between the 2 save points.