Hey I recently completed DS2 aswell and started doing Vorkath.
I'd say just practice and really get to know his attack styles and pay attention to when he's going to do his acid phase, which is every 14th attack.
This is my setup with my stats.
If I'm paying attention I can get 2 kills per trip.
And also for my prayer I have my quick prayer setup for protect from magic, and eagle eye. I usually only take 2 doses of prayer per kill.
I usually average around 2:45 per kill.
EDIT: I also equip a holy blessing for extra prayer bonus