Try disabling dynamic shadows, if this gives you a fps boost greater than 20-30 fps, then do the following,
Go to the LOD sections in each mesh, disable “Cast Shadow” on each material for All Loads EXCEPT THE FIRST ONE (for you lod 1 or maybe 0)
After this go to the main lights of your scene (the directional light aka sun) and set contact shadow length to 1.0 or fine tune it to your likings, and see if there is a perfomance boost, this works for me a bit not too much tho,
Thanks
Lonely