If your store is running slowly then there is a really helpful tip to help speed this up.
What you will need to do is: login to your OC store as an admin.
1) login to your OC store as an admin.
2) Go to System > Settings.
3) Navigate to the Option Tab.
4) Change the setting 'Category Product Count' to No.
5) Save the settings up the top right and then reload your store for increased performance.