Yea wait till you do the LAX-SIN 18:30 hr nonstop...I have done (as many have here) that 5 or 6x and after getting 7 or 8 hours of sleep, just movies, reading, staring at seatback infront of you, etc. So 15 hrs isn't so bad after that.
I really wish Boeing would pick up the Sonic Cruiser program again...