This is a paid asset, but now you can download Classical City : Mobile Free.
Detail this asset from Unity Store: Original Link
Classical City Mobile v1.0
This package contains a city area based on modern classical theme. This is mobile optimized having low draw calls and low triangle count. It is easy to use. Average triangle count is of each building is from 600 to 1800 tris.
There are 91 unique props prefab are included to use. Those prefab contains buildings, trees, props etc.
Package includes
complete city scene
Three Lighting condition
Three skybox
Rain Drop, Rain, smoke particles
13 background building
23 detailed building
14 trees and bush
40 props
Materials are easy to change. There are only 10 materials has been used for the scene. Road Textures is 2048×2048 and others are 4K resolution.
City models are in single mesh and divided in many parts to reduce draw call