It seems the example you refer to is missing. Generally, the more visual elements are to be displayed, the slower the loading will be. I can suggest you going through our online documentation on possible reasons why there would be degraded performance with it.
You can also open a new support ticket and attach a demo project there.
Check out the Telerik Platform - the only platform that combines a rich set of UI tools with powerful cloud services to develop web, hybrid and native mobile apps.