Depends on where the 2D geometry is going. I think there is a setting that allows for the user to turn off the 2D constraint engine to work on large 2D data sets.
I projected them in sketch and remove original imported data but still slow when trying to move, copy them. No problem working in other features of my project with the 2D data loaded in screen, as long as I am not editing the sketch. The sketch is a plant layout. Not a big problem but it is strange that this drawing which was quite small and easyly handled in dwg is so slow in NX maybe it is beacuse NX imported a lot of splines insted of other kind of lines.
I would do an "info -> Object" on a representative sample of the geometry - see what it is.
Like you say, possibly a change in the DWG inport settings could make life easier...
Production: NX10.0.3.5 MP16/TC11.2
I'd rather be e-steamed than e-diseaseled