Yes, for the tires, make it just a plan cilinder and add detail with the diffuse map. There are also some scale issues i think, the truck looks too big for the scene or something.
The bottom level of the fire escape SHOULD NOT be lowered. That's a robbery in progress. More dirt of course (especially old newspapers and fast food cartons). You can never have too much dirt. Is this a modular setting where dirt and lighting would be added separately? By and large it looks pretty good for what it is, but…
Can you also post wireframe of the entire scene? If it's 12k tris with or without truck (it almost doesn't matter), it seems like you have a ton of wasted polies there too, since your scene is mostly composed of boxy shapes, so I can't fathom where all those polygons went. An occlusion pass would help a great deal to…