1. Better optimization, there is no way this game should be running this stuffty
You realize that this is really hard to do?
The game's graphics are pretty much 16x16 textures, yes.
But for
every chunk loaded it literally eats up your RAM.
That's the cost of making a game with Java (Notch was probably high off his loving socks when he started coding, and just started working in Java for some reason).