Did you use the "Save" function in CC3 or did you print them as PDF?
Because the "Save" function is very slow for me as well and CC3 keeps crashing. Now I use PDF Creator and I can render maps in insane dimensions (think 15.000x10.000 pixels or something). It might take a few minutes, but it never crashes. My PC is also a couple of years old.

Before I found this solution I was making screenshots of the map in CC3 and then pasting all those screenshots together in Paint Shop Pro. It was rather awkward and very time consuming.