From the screenshot you provided it seems you have a lot of appointments visible at the same time - I counted about 1200 appointments. This generates a lot of visual elements and so many elements in the VisualTree makes the layout really slow. The only thing I would suggest you is to change the MinTimeRulerExtent to some value big enough to show a horizontal scroll bar. This will activate the ScheduleView UI virtualization and will greatly improve the performance. I would advise you to keep the appointments visible at the same time to not exceed 300.
Hope this helps.
the Telerik team