How to reduce file size of a large scene fbx unity

I have started Googling for information but so far no luck. There really isn't that much in the scene (180 low poly buildings, a couple or roads) This just happened to a, earlier version of this project. I have a situation where I just opened a project and got the following error (see end of post) While checking the size of the folder and files I see that a scene, the only scene is at a file size of 4.1 GB.

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How to reduce file size of a large scene fbx unity