that is ok. A file gets 1.5 to 5 times bigger when it is shared with TW 2.0.
Take a look at archicadwiki.com > Teamwork
EDIT:
Oh, just saw, that you ar eusing TW 1. Then it is NOT normal. You should compress the file by ArchiCAD automatically
Holger Kreienbrink
Director Product Intelligence
Munich, Germany
Archicad since Version 5....
If I sound too harsh, please forgive me: I am German.