They can't optimize the engine because it isn't theirs. It's a Cryengine, but old Cryengine 3 version. They can always make some optimizations, the only question is will they do it? For the next game, a sequel, the best solution would be to use Cryengine 5 cause it works much better and it's more advanced. But optimization also depends on how much effort you put into it, it's not just the engine. The good thing is that they have much larger team now. It's doubled now.