When loading QVD files, if you don't make too many changes in the load statement, the table will be loaded in an optimized form. Some changes are ok, like changing field names, while other functionality will break the optimization and cause the table to be loaded slower.
What Johannes said is absolutely correct, if you load a qvd without many changes then the data loads very faster. If we add any new fields, or modify any existing fields then loading would be bit slower. Check this URL hope it helps you.
