Doing game with no textures, problem with objects in shadows once more

I am doing a game with no textures, there is only one problem now, when i use one Directional light with shadows, it is obviously working outside of shadows, but in shadows, objects are only silhouettes (image 1 ). I had working solution from here, to add two directional lights (in opposite direction to each other ) with no shadows to have light in shadows of main Directional light. It worked (image 2 ) but it cuts performance. Like, i am not suprised, but is there any other way to get depth to objects in shadows ?

For example when i look at same building in same angle and position, with no lights 125fps, with only main directional light with hard shadows of medium resolution 50fps, with only secondary directional lights with no shadows 70fps (there are 2 of them) , with both main and secondary lights 30fps.

I strongly recommend looking at the light baking; when you’ve baked your lights and set your scenery static for the non moveable objects, you can delete all your lights and you still have super beautiful scenery with soft shadows and lighting. Baking is like taking a super quality snaphot of one frame and using it to lit every static object in the scene. You can have dozens of lights for the baking purposes. For the moveable object, just create another light and set the layers to illuminate those objects only.