Query execution-Master Paginated Report running with all sub reports

We have multiple paginated sub reports connected with main report based on the conditions, In that main report there are five parameters, we are using report name parameter for selecting the reports. when i select only two reports but irrespectively all reports are running in backed (sql query) and getting only what i selected the reports output. so we are facing performance issue .what we are trying to achieve if i select two reports ,we need to execute those two reports queries.