Report runs slow once subreport added.

There's a basic report with a few joins that usually takes less than 10 seconds to run to display some basic shipping information for the user. Recently I was asked to sum up at the end of the report a count of each SKU number. In order to keep from changing the groupings and doing any complex counts, I simply made a copy of the report, kept the query, selects, and parameters the same...but simply removed the excess information from the new copy of the report and made sure that it gave me that counts that I was looking for. The subreport runs in seconds (when I run it standalone) and the main report runs in seconds. But once I add in the subreport (in the report footer) it slows down all of a sudden. It takes nearly 5 minutes for the same parameters to run. I have not linked the reports so when I am prompted for the parameters I simply enter the same ones for both reports. Why does it take so long to run? I feel I'm missing some simple answer. Thanks much!