Large v. Small Meshes Performance

I have large buildings that are the focus of my scene. I would really appreciate some feedback and advice on how performance would be affected by having each building as its own large mesh versus each building containing many small meshes.

From my understanding, large meshes would not be efficient for background objects because even if only one part of the building is seen the whole large mesh will have to be rendered. Since the large meshes I am considering would be the focus of the scene most of the mesh will be seen at all times. Also from my understanding, draw calls will decrease if there is only one large mesh. Would appreciate any advise on things I should consider to best optimize performance. Thanks!