To get a realistic measurement of how your query tuning improves query response time you should start from a common point. To help with this you should clear your query cache before running a queries after making improvements (Unless you are cache warming of course !).
Here is some XMLA script to clear the cache for a specified database.
<Batch xmlns="https://schemas.microsoft.com/analysisservices/2003/engine"> <ClearCache> <Object> <DatabaseID> database id </DatabaseID> <CubeID> cube id </CubeID> </Object> </ClearCache> </Batch>
Replace database id and cube id with the details for your cube. Notice these are ids, not names. Look in the Analysis Services properties windows to find the ids.