If you're finding it a little difficult to go onto your heel edge, put less angle on the back binding.
If not, then just keep it how it is. It's about whatever feels best for you.
A good way of finding your stance is to put your boots on and stand on the board with them. Whatever stance feels the most comfortable in your riding direction is where you should mount them. Just make sure the distance from the tip of the board to the front binding is greater than or the same as it is for the back.
I used to ride -15,15 but I had trouble turning on my heel edge, so I changed it to -6, 15. Worked great after that. I don't know what happened during the off-season, but when I tried on my board again recently it felt uncomfortable. I changed the front angle to 21 degrees and now it feels nice again.
So, it doesn't matter what your stance is as long as it's comfortable for you and allows you to ride effectively.