There are a couple of things that can slow down reports in a .NET application.
1. The first time you run reports in general, it will take longer to load because there are several Crystal assemblies that have to load into memory. This part of the load time will go away with subsequent calls to reports as long as the timeframe between report loads is shorter than the garbage collection timeframe where the assemblies will be unloaded. There is nothing you can do about this load time.
2. The number of pages in the report - when you view a report in Crystal, it generates 1 page at a time, when you view it on the web it has to generate all of the pages in memory before it displays the report. This time will also increase if you're using things like "Page N of M" where it has to know how many total pages are in the report.
-Dell