Pattern Makes Model Heavy?

Depends on the topology of the holes you are adding. If all the holes are pretty much the same geometry (go through the same surfaces, no partial holes, etc.) you could look into doing a geometry pattern rather than the default pattern. Try doing a search on "Creo Geometry Pattern" and you'll find a multitude of other discussions of this or very similar questions.

Is the problem with model display or with regeneration?  If it's related to regeneration, under the Options tab in the pattern definition, try changing the Regeneration Option from General (the default) to Variable (better) or Identical (lightest).  These other options assume varying amounts of similarity between the holes to speed things up.

-Doug

As others have already covered the pattern options, here's a few tips you can try to optimize graphical performance:

In the display options menu (File>Options>Model Display):

• Uncheck the Shade very small surfaces option 
• Uncheck the Show textures on shaded model option
• Uncheck the Enable transparency option

Here's a mapkey that toggles these settings on and off. It works well if all the previously mentioned settings are on by default. That said, you can set some of them to be off by default by adding the config options. 

!!!Large assembly mode
mapkey LAM @MAPKEY_LABELLarge Assembly Mode;\
mapkey(continued) ~ Command `ProCmdRibbonOptionsDlg` ;\
mapkey(continued) ~ Select `ribbon_options_dialog` `PageSwitcherPageList` 1 `DisplayLayout`;\
mapkey(continued) ~ Activate `ribbon_options_dialog` \
mapkey(continued) `DisplayLayout.skip_small_surfaces.lay_instance` ;\
mapkey(continued) ~ Activate `ribbon_options_dialog` \
mapkey(continued) `DisplayLayout.texture.lay_instance` ;\
mapkey(continued) ~ Activate `ribbon_options_dialog` \
mapkey(continued) `DisplayLayout.transparency.lay_instance` ;\
mapkey(continued) ~ Activate `ribbon_options_dialog` `OkPshBtn`;\
mapkey(continued) ~ FocusIn `UITools Msg Dialog Future` `no`;\
mapkey(continued) ~ Activate `UITools Msg Dialog Future` `no`;