Average time assigned to Reporter- Query too complex

Hi,

I need to calculate the average time issues are assigned to specific reporters.
I created a calculated measure which should give me the correct result, but it always times out.

I tried removing all Page dimensions, select only 1 reporter and limit time to last week, and it still times out.

Could someone help me simplify this query please?

Avg(
Filter(
Descendants([Issue].CurrentHierarchyMember,[Issue].[Issue]),
-- time assigned to reporter
(
[Measures].[Days in transition status],
[Transition Field].[Assignee],
[Assignee].[User].GetMemberByKey(
  [Reporter].CurrentMember.Key)
 )>0 
AND
[Measures].[Issues created]>0
)
,
-- time assigned to reporter
(
[Measures].[Days in transition status],
[Transition Field].[Assignee],
[Assignee].[User].GetMemberByKey(
  [Reporter].CurrentMember.Key)
 )
)

Thanks,