Yes there is a file size limit in Si2013. With Si2014 upwards you can safe files up to 4GB, in 2013 it probably was only 2 GB.
Have you tried loading everything as Alembic instead of fbx ? Freezing the geo after importing. Making Quads out of the polys. Deleting unused clusters (normals and whatever). 55mio doesnt sound too much to me, should easily fit into a 2gb scene.
