Micropoly setting of 0.6 and AA5 and Pre-pass supersampling which resulted in a render time of 12hrs 50mins 33secs.
Curious what resolution and hardware specs were you using to get such a high rendertime. That's extremely excessive. I can probably help you cut that at least in half in not more depending on your hardware
Was actually rendered in 4K on an i5 3470 with 8gb... Can you perform any miracles? Water into wine? Loaf and fish multiplication?
I am currently waiting on a delivery of a new lot of memory, but as my motherboard only supports 16gb.... It won't do a whole lot, not sure if I was ever falling into the using swap space issue but I'm fairly sure it was close. Any worth while CPU upgrade would involve a whole new machine and the best part of £1000 which I don't have... So miracles?
Nope, no miracles. I actually have questions for you in regards to your render settings, because there is no way this scene should take 13 hours to render with the hardware specs you provided.
What are the sample values in the atmo node as well as cloud layers?
Are you using Defer Atmo? (Raytracing)
Are you using Soft Shadows? If so what are the settings?
What are your GI settings? Srf
These are the normal culprits for excessive render times, if these are ok then we can dig a bit deeper. 13 hours is too long something is set too high/incorrectly