I can't tell from your screenshot how many entities you have, but given your description, you have too many. Merge multiple entities into one single entity and the problem should otherwise go away. Rather than 8 low-detail buildings, merge them into a single model file instead. Also, having multiple skins per model shown at once will also cause a slow down. Merge the vertices as well as vertices have a huge impact on the frame rate. I've proven that, if you swap the vertex and poly counts, the one where the vertex count is higher takes twice as long to render than does the one with the poly count being higher.

What are your system specs and what is your nexus setting? If you only have 256 MB memory (like a typical budget system would have) and have the nexus at 64, you're almost certainly going to have problems with speed.