Hello folks,
Long-time user of Vegas here, recently upgraded from 14 to 15. I like the new UI, but it turns out it has severe issues. With every action you take,such as adjusting your layout, switching tabs, etc., parts of the interface will become more and more unresponsive. This happens extremely fast; less than ten seconds of messing with the layout are enough to reduce the pan/crop interface to a crawl.
You know the adage, a picture says a thousand words, so I made a video that showcases the problem:

I'd consider this to be a fairly big showstopper in terms of usability, so I hope this can be looked into.