Don't forget to take into account the effect on the Saver's Credit.
If you think you'll be paying more than 15 + 6% on withdrawal, then yes, go Roth. If you think you'll be paying lower than that on withdrawal, then no, stick with traditional.
Well, that's the $1M question...Even if our tax bracket is the same/slightly lower in retirement, the fact that compounded earnings won't be taxed would still make a difference. But would it be material enough to make it worth the hassle of the recharacterization of the already-made 2015 deposit, and the conversion of the previous balances?