Rendering smoke size issue appreciate you taking the time!

So I have a simulation of smoke that I'm using for the engine of a spaceship, my problem is that I can't feasibly see how I can render it. 

A single frame on 1080p/300 samples in cycles (on the more demanding frames with the most smoke) takes 1 hour 35 minutes. which works out at around 20 days render time for the whole thing.

I have a huge amount of points on sheepit renderfarm but I can't use them as the max upload file is 500mb and my smoke cache is 4.5gb.

Is there something that I'm doing wrong? Please let me know if you need additional information. And any broad guesses at common size issues are very welcome!

Cheers guys!
What are your numbers on the volume sampling step size? You could try reducing it, you won't lose any significant quality, check out this other thread, it might help

Smoke drastically increases render time