Update: on the basis of this thread, I have opted for BR11 instead of BR15 on recent LAX-TPE flights. I will note, however, that my experience in J was pretty much the same. I have not been able to tell the difference in the J cabin seating or condition between BR11 and BR15 flights (with the exception of the missing lavatory as pointed out above and the newer IFE system --- although since it's an overnight flight I did not use the IFE much at all). Crucially, however, BR11 is indeed more full, with fewer seat selection options -- and on my latest trip, more young children in the J cabin (thank goodness for noise cancelling earphones).