I'm rendering a very small animation right now. I left out the clouds and the trees for testing purposes. I could shorten rendertimes a lot by decreasing the radius of the localised cloud that represents the mist. It was way too large. But I realized that I have to check "receive shadows from surfaces" in the atmosphere's tab as well, because the sun is visible through the columns.
Some other ideas: I'll try to animate the mist (very subtle, not too much) to make it look less static. And I'll do some tests to animate the olive trees by using the mesh displacer. Maybe I can restrict the movement by the height control of a distribution shader?! They are all standing on the same level. They are single objects, no population.
And then there are the birds. I have the animated obj sequence, but it may be a problem to place them in a way that they don't fly right through the walls or columns of the temple.
Wish me luck!