Imported Blender meshes, added Unity box colliders - scene goes choppy, slow.

The first thing I thought of when I saw Unity's terrain editor was "open world." However, after having imported meshes created in blender into scene - a town located on an island across a bridge - the scene is going really choppy and slow.

The meshes are, for the most part, unfinished rapid prototype placeholders - actually less complex than the finished are to be.

For virtually all meshes, I've placed simple box colliders. Yet, the scene is running choppy and slow - and thus far all I have placed are fence meshes, a few prototype building meshes, a cemetery, a gravekeepers shack, a cafe some barrels, shovels, crates, pots, bottles, candles, rope, sign post, tables, chairs, beds - and some papers.

The system I'm using is an AMD 4200 with 2Gb RAM, 512Mb Radeon HD2600 graphics card.

Any solutions?

Maybe you have mesh collider generation on for your level?