It doesn't as far as I can tell--no matter what I pick, it's an immediate crash. Am I missing something? I'm totally humble when it comes to asking for help!
I had same issue with several NewBluFX plug-ins and the only way to solve it was to refresh Vegas Pro by holding down Shift+Ctrl while starting. Beware you will lose all individuall settings this way (including self-made presets).
I have Hitfilm Ignite 2016 pack installed and the ones I tested are all working OK in Vegas Pro 15. Can you supply a specific example for me to test? Which Hitfilm plugins are crashing?
Maybe you should try un-installing your HF plugins and re-installing from fresh download. Make sure to re-boot your computer, then do a full program reset for VP15 again.
What model Graphics Card and Driver are you using?