You have to realize that not only are performances of nacl probably going to improve with time, but more importantly this is not a port of the game in nacl, this is a port of the game, running in the dosbox emulator running in nacl (Dosbox emulate a whole old computer, which then load the game). Redoing such a game from scartcg in Nacl and getting rid of the emulator layer would have much better performances.