Low performance on the Piwik UI

I’m trying to figure out why does the Piwik UI works so slow.
It monitors a site with traffic of about 20,000 visitors per day,and the screes load so slow.
All servers’ system parameters and Piwik DB show good performance, so it seems like something in the interaction between the App and the DB.
Also, the ‘Log Visitor’ module gets stuck on entrance. Is there any configuration for pagination in this module?