To build on what Dale said, if you make the polygons all use the same texture, material, and keep the polygons white, it will make things render much faster. If you can make all the polygons on say, an airfield, use one texture and one material, it would render fast and you could actually use more polygons.
Also in regards to your tower object, you'll lose all detail you have on those handrails beyond probably 20 feet max. After that distance, you may as well make them flat polygons or wireframes. Moreover, you have to think about whether or not some of the details are worth making. When a player is flying by, they're not going to be flying by admiring your handrails or the fact that you made a guy standing on deck drinking a cup of cocoa with modelled marshmellows floating on top.
Most likely, they won't really notice much of anything beyond the general shape of the building. If they're close enough to notice such details, they're about to crash into it.
