Just went through this at Pismo Beach last week. When I got there, I initially aired down to 30psi for the drive from the entrance to the campsites. I turned in towards the dunes and got stuck in about 50 feet. A regular in a 4x4 hauled me to the top of the small hill and I tipped him $20 for his trouble. I was able to drive a little ways further on my own. Over the course of the next day the wind blew in so much sand I ended up burried in a hole. I aired down to 15psi and shoveled enough and much to my surprise, I drove out with little effort. I drove down to the beach, maybe 150 yards and then proceeded to air back up.
I wouldn't drive very far at 15psi but if your stuck, it's an option to give you the float you need to stay above the sand.
A couple of notes... Get some airdowns on Amazon to help speed the process up and also buy a good air Chuck that stays on the stem on its own. This will save a lot of effort in deflating and inflating the tires.