Smoke in scene

I’ve been rendering out the smoke alone on one of the machines here at my student house (one of my housemates is away and letting me use his computer as a render node). the 2nd image is the smoke rendered out on its own and the 1st one is the smoke composited into the film (by Moe). The shortest frame to render is around 2 minutes, the longest frame takes as long as 25 minutes for the smoke alone.