My PC is pretty old and has a pretty poor performance too, even worse than you. Can't really suggesting that much games since I'm mostly playing singleplayer games, but how about Closers Online? It's similar like Elsword and if I recall correctly the maker is the same like who made Elsword.
Well, actually I never tried it before since I think my current PC can't run the game smoothly, but lately the game got it's CBT in my country.