Play Prologue on new game!! I suggest waiting at the first bridge after the one is destroyed by the tie fighter. they will keep jumping over to it and seem to spawn a little longer for I kept running out of them before the cheevo would pop but it may just be me.
Change difficulty to sith master because Vader can not die in the prologue and you will have less chance of killing enemies with saber deflect! Also if they enemies stop spawning like they did for me just leaving you three random dudes coming every once and a while make sure to save and then quit and pick up on last checkpoint because it will save your kills.