I would think 10 psi would be fine. I'd try going down to 12 psi first, see if you lose a bead while wheeling. If not, try 10. It really depends on the wheels.
I had a 35 X 12.5 on Mickey Thompson Classic II wheels and I could go down to 9 and not lose a bead. Then I went to 37's on different wheels (17") and couldn't go below 11 psi.
In your situation, if I couldn't go down to 10, I'd get different wheels, 15X8. Mine isn't a DD though.