Couchbase Sync Gateway Shadowing

Hi

Were using the Couchbase Sync Gateway shadowing funcitonality.
When uploading about 14,000 records to the main bucket - it takes an enormous amount of time for the Sync Gateway to update (more than 1 sec per doc)

Can someone please elaborate on what performace factors the shadowing method relies on and what can be done to enhance them?

Thanks
Arik