Running reports in CMC is Slow (the first time)

when we first log into CMC - the report takes 10 minutes or more to run.

when you run it subsequent times - it takes less than 15 seconds...

what could be causing this unbearable delay the first time?

I've seen some people say that you should build a blank report that users can run first - that is not a solution....

Has anyone had a similar experience?