One way to get close to what you want to do would be to create several Project, one for each Sequence, and then Import just the chosen Sequence into that, and do a Remove Unused, so that each discrete Project will only have the links to media used in that one Sequence. When done, you can create a new Project, and then Import each of those separate Projects/Sequences into that.
There is no way to make Premiere Pro load only part of a project. However, that should be unnecessary. You don't have to wait for everything to load to start working. If the clips you need are loaded last, then you will. But if what you need is already there, you can work while the rest load in the background.
PP is alao a pretty stable program (at least on a clean install of Win 7 it is). If it's crashing a lot, you may want to solve that. It isn't normal.
Finally, the number of clips in a project will not have any effect of playback speed. If you aren't getting real time playback, something else is the cause. You may want to solve that as well.