The first time you preview your solution, Stadium takes some time to build and render your solution in your browser. In order to speed up your preview experience, do not close your browser preview tab. Keeping your browser preview tab open, will help Stadium to only update the changes to your browser instead of rebuilding the whole solution. Thus, the rendering time will be less and your browser will be updated instantaneously upon a refresh.
Note that if you change your startpage of your solution, you will need to close the browser preview tab and preview your solution for the change to happen.