Regarding texture size, 4k might be justified for when the single tile of the pattern is viewed across the entire 4k screen. This might happen with a large stone slab on the wall, but usually this is not the case. Using the free SU Material Resizer Plugin can help quickly reduce the images that do not require such high resolution. I usually use 512 or smaller for patterns that never get close to the camera or are small and repetitive, 1024 for items that need a little more detail, and may allow 2 or 3 as needed to push 4k if they are an exceptionally large materials that the camera gets close to and that need to show more detail.
You should make a copy of your file and experiment with the reductions until you get the level of detail needed with the lowest amount of pixel data possible.
The other way to reduce file size is to examine your components and modeling techniques for polygon count.
You can use plugins or use MeshLab to reduce the number of faces on components.
Again, get it to the level of detail needed for each object depending on how close you intend to move the camera to those objects.
Hope that helps.