Erasing unseen meshes of objects for performance boost

We’re using an ortographic camera in our game. We’re wondering whether erasing the meshes of the unseen parts of the (immovable) objects provides a performance boost or not.

To be precise, we’re trying to figure out whether Unity renders those parts or not in the first place, and what we see in the game are fully rendered objects or not. Any provided documentation or source to be read would be greatly appreciated. Thanks in advance.

As far as I know, it does render unseen faces so if you have faces which are never going to be seen by the player, you may as well remove them from the model.