Crystal Reports multiple subreports

Message

   Hello, I am creating a large report (600+ pages)
for each page I will have 1 of 6 sub reports displaying depending on the group.

I though Crystal would not run a subreport if it is suppressed?

If I have one subreport that runs for all 600 pages it takes 8 minutes,
as soon as a add the second subreport suppressing either one depending on the page, it takes 17 minutes. and again with the third it takes 26 minutes.

The number of pages does not change in the main part of the report (600)
Then why does the time double when I add an addtional subreport when I am suppressing the other?

Thanks for your help...