Usually the issue is related to where the file is stored. If the file is being accessed over a network it can be too slow. Another possibility is the file is on a spinning hard drive rather than the internal SSD. It is going to be much faster on the SSD.
Beyond that it can be slow if a lot of reports are open and you have modified the setting to allow for live report updates (rather than having the refresh button). That's in QuickBooks->Settings... in the Reports section.
If none of this fixes it try File->Utilities->Rebuild. Sometimes the data base Indexes get wiped out and this will recreate them.
