The XAML editor, in its default setting ,at times takes a while before it becomes responsive. As I usually don’t use or rely on the Design View this seems counter productive to me. A way of speeding up the XAML editor is going straight to the Source view. To do that go to Tools -> Options -> Xaml Designer. The image below should show the default view.
The Default document view shows 3 options. As shown in the image below
Select the Source View and click ok