some observations of mine:
* turn off all transparency you got. It was or is meant that Creo handle it better, maybe, but regarding time of refresing/opening, nothing changed.
* try to save all external data like iges, or steps as prt files. That is strange but same part can take ages to open when retrived as STEP, being opened in seconds while saved as Pro/Engineer model.
* check if all your files are in the same directory. While search.pro can fix retriving files even from network resources this can invoke opening delays, while it starts to be depended on network conditions and so forth. I met it many times, same machines, different opening time. Cause of the problem - standard parts retived from network storage.
* display settings - set them down to minimum. two machines different display settings and you can get what you have: machines chokes while opening.
* complicated sketches or cosmetics - well, if you have a lot of text notes done in sketcher or cosmetics, then the problem is there. These "tiny" features make Pro/E crazy, because they are parametric, and they consist of many small entities which Pro/E tries to regen each time and over
* cut outs operation made in assembly mode - while opening the assy pro/E must check what, where, why and how. refuse such solutions
* if your assy consist of sub assies, open each of them separetly and check which one takes longest to regen. then focus on it, evalaute, find the cause(list above), fix it.
* and so forth, and so on....