Ran into a performance issue for an end-user today where the Send/Receive process was hanging on synchronizing subscribed folders.
One method to help speed up this process was to disable calculating the number of unread items each in subscribed folder that are synchronizing.
Click on Send/Receive tab in the Ribbon and then click Send/Receive Groups and choose Define Send/Receive Groups
Click Edit in the right pane
Uncheck Get folder unread count for subscribed folders and click OK