converting a prefab to single .fbx of .dae with textures

hello guys , i dont know if its possible or not it is like a silli question please dont laugh after reading it . I have a scene that contain two prefabs not exactly two but for example take two okay. Each prefab contains 6 or seven different prefabs and all of them are 3d objects with textures. so on running scene everything works fine but what i am thinking is that is there any way to convert both of that prefabs into two different files like .fbx or .dae so as to optimise the scene because after conversion the whole prefab will act as a single exported model file and will reduse work load on mobile devices . Is it possible or not ?? if possible then how ??