Hi
There are various levels to which you have to check to improve the performance of reports could be at connection levels, query, database etc.
some of them you can try
1. check array fetch size in relational connection parameters, deactivating array fetch size can increase the efficiency of retrieving your data, but slows server performance.
2. Setting options for the default list of values in business layer and data foundation layer
Automatic refresh - If this is selected, the list of values is automatically refreshed each time the
list is called. This can have an effect on performance each time the list of values is refreshed. You should disable this option if the list of values returns a large number of values.
3. set query stripping (Optimize query with Query Stripping in Web Intelligence - Business Intelligence (BusinessObjects) - SCN Wiki)
4. also check Performance Tuning Methods in BO
Regards,
Raghava