Hey rafpug,
I got your scene and went through some optimization..
First of all I merged your scene from scratch in order to make sure there were no "wrong" values in settings to start with.
In render settings I used PT+PT, which is faster from HD since its an exterior scene, and which yields more physically accurate results as well.
I set "Path tracing samples" to "24" and used "Bucket" mode with a setting of "3" for both "subdiv AA" and "adaptive steps".
"Pass Limit" was set to "1" since I define the level of quality under "Bucket" settings.
I also set "Max ray depth" to "64" even though increasing it seems to introduce some kind of a visual glitch in this specific scene caused by some light trapping on the left chair.
General rule though concerning "Max ray depth" is that in order to get physically accurate results you need to increase this value until a point is reached where increasing it further gives the same result as before.
Examining a bit further the above I noticed that the IOR (Index of Refraction) of the material used for the chairs was way too high ("5.00").
There are no materials in real life with such high IOR apart from metamaterials which are artificial and subject of a whole different story..
This setting is also what caused such great impact in rendering time when you increased "Max ray depth".
Seems to me like there was some kind of endless looping that were caused by some trapped rays due to such high IOR.
I set it to "3.00" which I believe is still too high for the material you're trying to achieve but I didn't want to deviate too much from your settings.
Furthermore there is no actual need for the "Falloff" maps you connected to reflection and refraction to simulate "Fresnel" since the IOR value does about the same through a more physically accurate approach.
I also made the actual sun disk invisible in reflections and refractions to get rid of the fireflies..
Apart from the above changes, which seemed a bit obvious, I didn't go into a deeper optimization
however these changes alone had an enormous impact in rendering time and a better refined image..
Since though this thread is about animation, there are ways from which faster results can be achieved,
for example by reverting all values under render settings to default and using Bucket mode with "Subdiv AA: 2" and "Adaptive steps: 3" gives an acceptable result in under 5 mins..
Oh and talking about speed, I'm using an overclocked Core-i7 @ 3.5Ghz (the render stamp can be deceiving).
I'm uploading the previous result as well for the sake of comparison as well as an image with a different material for the chairs,
I believe it's closer to what you might be trying to achieve..
Hope all the above will prove helpful in any way..
Cheers..