if you are using glass, turn off refraction. you don't need it. I suspect the sheer number of lights is your biggest process consumer. you've got at least 30-40 of them. Definitely check for soft shadows and volumetric effects. The trees won't help either if those are the generated trees. You'd be better off using a picture on a plane, or adding tres in post. You could also try rendering them separately and compositing them in post. Your vehicles are small enough you could get away with a single headlamp spotlight for each. try using glow maps instead of light sources for some of the areas, like the walkway and the elevator shaft. Add the smoke in post. If that is a volumetric material, it is a processor pig, esp. with 30 different light sources hitting it. The water does not need to be refractive, or even transparent in this scene. Maybe consider even rendering the rooftop separately from the rest and compositing later. Try attenuating some of the area lights and headlights so that they are not all being calculated in the entire scene. Also, some of those lights don't need shadow casting turned on. Lights without shadows are MUCH faster to render, so play with that a little. Hope this helps.