In my experience, 142,152 actors is a HUGE number for Unreal. Dynamic lighting for that many actors is also going to be rough. The best thing you could do is reduce that number as much as possible. I usually spend some time in Rhino meshing and joining objects before importing. If you can get a nice script together to automate that, it only takes a few minutes and can drastically reduce import time. For example, if you are importing a lot of buildings, and each window is a separate object in each building, it might make sense to join all the windows together (per building side, per entire building, or maybe even per block) into a single disjoint mesh.
If you are primarily concerned about import time (for example, it you are trying to do a quick initial test import), you can also reduce import times a lot by not importing materials and by lowering the lightmap uv resolution on import. This might not work for production-quality, but In our workflow for example, we replace all the materials anyways, so I don’t usually import materials.
A very simplified note on optimization: The number of different meshes and materials increases the number of draw calls, which is handled by the CPU. On the other hand, the number of polygons and dynamic lighting affects the rendering time which is handled by the GPU. Which one is the bottle neck for you will depend on your machine and set up. For statically lit scenes, in my experience I usually hit the draw call bottleneck first.