Optimizing Reflect

Hi! I was wondering if is there any process to optimize reflect performance, I have to set up really huge proyects (like entires airports or kilometers of railing and train stations) and in others computers its performance is too poor (it gets very low fps)
By now I have been setting up the quality settings, baking lights, and those little things but i will need more...
I have been reading about combining meshes, I thinked this could be a good option but I´m a bit frightened with the posibility to lose some metadata or something like that.