When filling in assignee.name on IM.update.incident takes almost 10 seconds to return list

All,

 

I'm trying to investigate a performance issue.  While on IM.update.incident and hitting the fill button for assignee.name it takes up to 10 seconds for the operator.qbe.g to be displayed. 

 

Any ideas where I can look or what query is being passed to the database?

 

I've looked at the  probsummary link record for assignee.name and this appears to be the same as oob version which returns list in 1 to 2 seconds.