I couldn't render it in Vue6, for comparison, because the scene was saved in Vue7. Anyway, in Vue7, in a quadcore machine (VueMark7=103) the scene rendered in 1m40s, which is a lot for such a simple scene (GI, spectral atmo, spectral1 clouds and 1 cylinder with displacement).
I immediately noticed the culprit for such slow render were the clouds. I disabled the clouds and it rendered in 5 seconds. I added some standard clouds ("Low clouds 3") and the render time was 8 seconds. So, conclusion is: it really pays to search for the right clouds! :-)

Anyway, I went back to the original clouds and did some more tests. I decreased the quality slider in "Clouds, Fog, Haze" tab from 1 to zero. The render time was 1m08s. There's no significant difference in quality. Then I decreased the quality slider in the "Light" tab to -2. The render time dropped less than I expected, probably because of the simplicity of the scene. The new render time was 1m04s (6% drop).
I decreased the quality slider in "Clouds, Fog, Haze" tab to -1 and the new render time was 45s. The clouds start to show some signs of the low quality slider (some grain) but it's still ok, I would say.
So, conclusion is: if you really want to use those clouds and still have good render times, you have to significantly decrease quality slider in "Clouds, Fog, Haze" tab.