trust me, you need a much larger 'roll than 15k to play 600 NL 6-max. The swings you will get are insane. I would recomment a bare minimum of 25k. Im playing 200 NL 6-max with a 17k bankroll and I dont feel like I have a big enough 'roll to move up to 400 NL quite just yet. High stakes 6-max is very swingy and forces you to not ever play with scared money as you got to put your whole stack on whims. So you cant play with scared money.