You can improve your Koken site performance by making sure that KeepAlive is enabled. KeepAlive is a webserver feature that allows the transmissions of several files at the same time and not one after another. For this you could edit either your webserver config (fe. apache or nginx) or just add the following lines to your .htaccess in the root-folder of your Koken-installation.
You can find more info about KeepAlive here