I've never had any troubles with vray + ab.
The only thing is, it takes a fair while to calculate the GI on the puffs

which is really cool for sure but it is a major time waster when you can simulate it yourself.
If you're using default settings in vray and afterburn it makes sense that it will go slow. These days I barely use GI in vray, I just make my own lighting. GI is cool and all but it does eat away at time. You shouldnt scrap objects in your scene because they take too long to render. Just find a different way to render them.
Try turning off the GI, and seeing how fast it renders. Then try turning off the AB, then reducing smoothing amounts and doing things like that in a step by step process, and see what it is causing the delay, and then try and rectify it.