Oh yeah, I remember sand like that.
No way that'll work with a smaller tire.
Consider 5 PSI as a starting point. (going by feel is actually not a bad technique, If i can push to the rim, I add a few pumps)

As for those stickers... (burrs, thorns)
Good luck. Hated those things. Probably won't pierce the tire, but consider a patch kit and pump just in case.