Let me check:
It’s 2:16 on 1280x720, frame 70 (I am having intel i5).
Maybe it’s fast, because I am not using Vray GI (I am using vray ambient light, and within map, I’ve placed vray dirt texture, so I get some GI fake, and AO shadows).
Apart from ambient light, I am having default spotlight (for volume light) with default shadow map, 1 vray plane light on the exit, and 2 vray sphere light on the left (one for character only).
Why don’t you try to render your volume light in scanline (just make everything “matte/shadow” material (and make sure you check “apply atmosphere”, and "at object depth), and just put that pass in after on “screen”, or “add” blending mode?
I might do it also, because I am not sure, I’ll be able to render all in 720p, by the deadline.