Love the idea and render, but if you are open to a suggestion, in Shading rate. lower it to 0.010 you will find the fine dots of the skin in the shadow's will smooth out and take your images leaps and bounds closer to a luxrender quality image. Keep in mind with your computer the render will still take longer. I'm guessing your image would take 45 minutes. do test renders of course first before dropping the shading rate to so low. Good luck.