Yes, that was my Bryce Flak Freebie that you are referring to and it was constructed the same way as this explosion.  One mesh and volumetric material for the smoke and another mesh and volumetric material for the fire.  With a light in the middle of it. 

Anytime you add the volumetric material, you will have increased render time.  Add transparency and your render time increases more.  Add more lights and your render time goes up again.  Want soft shadows?  Go ahead and add them, but the render time goes up even more.

Free men do not ask permission to bear arms!!