I'm currently using Vegas Pro 14 on my desktop computer running Windows 10. The problem seems to be with the preview window where you can view the project you are editing. Once I place a clip into the timeline and try to play the project, the beginning of the clip takes a while to start, but then runs smoothly. This makes fast edits completely unable to be viewed through the preview window. If i render the project there is no issue with clips lagging at the start.