For the NSC Shaded Model layout and NSC Object Viewer in non-sequential mode, your options include:
1) Reduce the number of facets in the “Draw” tab of the Object Properties dialog:

"Draw" tab of NSC Object Properties dialog showing "Drawing Resolution" (i.e. facets) settings 
2) You may also want to consider hiding objects which you do not need to draw:

 "Draw" tab of NSC Object Properties dialog showing "Do Not Draw Object" check box
(Note:  Rays will still ray trace and interact with an object, even if it is not drawn)

3) Increase the amount of memory on your video card or install a video card with more memory

Also, for the NSC Shaded Model, you can also reduce the number of “Layout Rays” in the Non-Sequential Component Editor for your source object(s):

NSCE showing "# Layout Rays" column for a source object