thanks for looking into this Minh.
i have created a new scene to test (don't think it's scene specific):
1. import image file reference and use as Trace Reference - performance (i.e. panning and zooming in.out with scroll wheel) is marginally reduced but still very usable.
2. insert Stairs object - with the Stairs object selected panning and zooming in/out with the scroll wheel becomes 'sticky' and delayed.
3. enter Edit mode on Stair object and effect of the above is even more evident. editing for example the shape of the stairs is much a more fluid experience with TR off but is laggy with TR on.
can you try the above please?
ETA: in trying the above, the Stairs object, or an element of it, must be selected for the delay to be evident.