I have the same experience upgrading from NXT2 to NXT7. NXT2 was constantly crashing and I had to save every time I made a change. I thought that an upgrade would take advantage of Windows 10, more RAM (I have 32GB), and be less prone to crashes. Unfortunately I was wrong. Task Manager was monitoring it as using 97% CPU resources. so I couldn't do anything worthwhile.
I finally used the compatibility setting to have it run as Windows 8, and so far so good. Task Manager shows it as you would expect a normal program to run. Best of all, I can actually do real work with it. Maybe if I had tried that with NXT2 I wouldn't have need to upgrade in the first place.