First of all, you need to stop using the card completely. Yes, that means you lose out on cash back, double miles, whatever, but that's how you got to this mess in the first place. Switch to a cash budget until you can consistently spend less than you bring home. Keep better track of your expenses, build an emergency fund, and learn to save for expenses rather than borrow for them until you have your spending under control. If you can't cut your expenses any more, consider ways to increase your income (more hours at work, part-time jobs, sell stuff, etc.)
Assuming that the employer match is 1-to-1 up to 4%, and you're saving an additional 7 percent to get to 15% total, I would definitely lower your contribution down to 4%, get the card paid off, and ONLY bump your contribution back up once you can safely pay off the card each month and know how much you can contribute.
It is not wise to put 15% in retirement if that causes you to spend more than your net take-home pay. Your "13%" in your Roth is not guaranteed by any means, but the interest you pay on your credit card is.
I would even be tempted to cut your retirement completely until the debt is paid, but more for motivational reasons that mathematical:
- You are motivated to pay off the card faster because you know that you are missing out on a match until you do.
- You will not see the benefit of the match until retirement (and have plenty of time to make it up) but you feel the pain of the debt now.
I would be more concerned about living within your income at this point than getting a company match. I believe the benefits of spending wisely will outweigh a temporary loss in matched retirement funds in the long run.