Do you have a lot of channels enabled? If you scan for channels, by default we select all of them as being enabled (which means they'll show up in your Guide and Live TV tabs). But having dozens of channels can slow down performance a bit. We recommend taking a look at your channel line up and, if there are channels that you really don't need, you should remove them so they don't show up:
Go to Settings (click on the little "gear" in the top right)
Select Guide in the dialog window that appears
Uncheck the channels you don't care about
If you want to re-enable them, just go back to the window and re-check the ones you want to add back.