Entities have no effect on your map VIS data size nor do detailed brushes. The only thing that adds to you VIS data size is structural brushes, sides of structural brushes that can't be seen by the player in game should have caulk on them. Because of that removing any entities will not help!
My guess is that you have to many structural brushes, only brushes that are potential visibilty blockers should be structural. Do you have any knowledge what VIS is? I have written a VIS for dummies tutorial, it might help you gain some understanding. The tutorial isn't complete yet because I'm going to add info about detailed brushes (for now all you need to know is that a detailed brush doesn't affect/add to vis).
Read the Vis for Dummies tutorial here: [url:970c6]http://w1.261.telia.com/~u26123488/vis/visfordummies.htm[/url:970c6]
Find more useful information about VIS here: [url:970c6]http://www.modtheater.com/forum/showthread.php?s=14c813532142ce3d814ac9fc5151def6& threadid=22[/url:970c6]
And make sure you visit
http://www.modtheater.com if you actually want to learn and need help with mapping.