A lot depends on the structure of your report, the number of records you're reading, and the types of sorts or filters that are in your report.
Since the report is reading a dataset, if the dataset is not filtered or sorted, all of that will happen inside Crystal after it has read all of the records. If you have a lot of records, this will take some time. One of the things that I highly recommend is that you filter the data that is read into the dataset when the query is run instead of relying on Crystal to do that for you.
-Dell