Did you load any textures with texture filtering set to none? That will cost lots of memory.

• Put all textures at quality or crisp. => U can use the free Scenefixer script for that.

MSR at 0.2 is the normal lowest setting. 0.1 is overkill and only costing memory.

Put:
RBounces at 2, is good. But you can use 1 if you have no reflections going on.
IC at 32, the default, but you can try at 0 (zero)
PSamples at 4, or even 3 => 6 is heavy overkill for a simple scene
MSR at 0.2 leave it there
Bucket size, 16 or 8 or 4 => decreasing will reduce memory load for slightly longer render time

Fastest?
RB at 1
IC at 0
PS at 3
MSR at 1
Bucket size  : play between 32, 16,8, or 4 (4 being the slowest but less memory hungry)

Optional:
Post filter size at 3 and on Type use sinc
GCorrection ON at 2.2

First check that ALL textures are at quality or crisp.

And a question?
What size is the HDR on the IBL light???? Set it at 256x256 pixels. YES, 256x256 pixels.
Too large a HDR on an IBL light is the fastest way to memory overload.. (I never use IBL or AO) => Allways IDL.

Poser 1, 2, 3, 4, 5, 7, P8 and PPro2010, P9 and PP2012, P10 and PP2014 Game Dev
"Do not drive faster then your angel can fly"!