Struggles to load menus

When accessing the menus, like adding a route/toggling Wifi etc. I always get the spinning wheel for a few seconds before the first menu loads, then it really struggles sliding over to the next pages. However, do it a second time and it's nice and speedy - like it's got it loaded into its memory now. 
This happens at any time, not just after boot up, so it's not under boot load.