a lil' tip, matey:
if ya don't know about it yet - learn to "createUnit" and such stuff
THAT is what REALLY keep the laggy missions off yer comp' back home!
You can create a single gameLogic and give it WP's, and then delete it right from start, replacing it with created groups... and those men will then follow the WP's that you made for the logic
(well, a very short introduction, granted).
In short, enemy groups won't appear on the map untill YOU hit a trigger (get near the place of supposed action etc.)
This way, ya don't need to create 10.000 groups in the editor (men and their orders is what causes most lag, as far as I know).