Hi Ste,
As per my understanding, the query execute in Query Designer is retrieve the data from the database. When the database is from another server where install SSMS (SQL Server Management Studio), the query will spend some time to connect that server. This will
make the query execute slower than directly in SSMS. If they are in the same server, the execute time might be equal.
However, the total time to generate a reporting server report (RDL) can be divided into 3 elements: Time to retrieve the data (TimeDataRetrieval), Time to process the report (TimeProcessing), Time to render the report (TimeRendering). So it will take more
time to render the report.
To improve performance of reports, we can refer to the following articles:
http://technet.microsoft.com/en-us/library/bb522806(v=sql.105).aspx
http://www.keepitsimpleandfast.com/2011/07/more-tips-to-improve-performance-of.html
Hope this helps.
Thanks,
Katherine Xiong