It took around one hour, gave Mitsuba 6 of my 8 cores.
Intel® Core™ i7-3632QM CPU @ 2.20GHz × 8

Used photomap integrator with recommended irridiance caching after seeing blotchiness on the first test pass.
Integrator - tried 36 samples per pixel for a test and then ramped up to 400.

Other options pretty much the defaults that Mitsuba supplies.