It seems impossible to the maps baker to handle very large geometry.
I have some photogrammetry mesh arround 100m polygons and 12-15go. The loading is very long and stop with an error.
I was hoping to do the maximum on houdini with the less other software, but i'm stuck on substance designer who bake this kind of geometry very quickly (a lot quicker than xnormal by the way).
I wonder if you have a solution for this, if not I really hope that in the future the maps baker work for this kind of mesh, it would be great.