Isilon poor performance with Excel sharing turned on

We have a dual site configuration where Excel sharing is turned on.  Once more than one copy of the file is opened the performance dives.   So, we tested.  We had the same file put on a Windows 2012 R2 server on one side of the country and the same file put on an Isilon in the data center on the other side of the country.  We then had  users in each location with identical loads on their laptops.   When the users in the data center opened the Excel file on the Windows 2012 server across the country, everything worked fine.  Same thing for the single Excel file being opened on the Isilon by the user in the remote office.  Once the second copies were opened, the Windows 2012 server worked fine and the Isilon copy began to perform very slow.  Am I dealing with an opslock issue here?