Mdx query too slow for few no. of records

We are using mondrian olap server and mdx query for our BI application. But in the profiler(yourkit), we see the application fires multiple sql queries which are group by the description column to show the report, though we have specified the primary key and foreign key columns references in the cube (xml file). We want to change this group by clause to id column. We are not able to do so.

Also it took around 8-10 mins to run. Its too slow to work.

This is my query

select NON EMPTY {[Measures].[Revenue]} ON COLUMNS,
NON EMPTY ({([Stream].[All Stream],[Portfolio].[All Portfolio],[Serviceline].[All Serviceline], [Year].[All Year], [Month].[All Month],
[Department].[All Department])}) ON ROWS
from [RevenueBudget] where ([Time].[201303] : [Time].[201508])

In the Db there are only 5,000 records.

Thanks in advanced