Looks to me like N-11. As you say N-15 always comes with strong obv denticals, and the reverse denticals are gone on both 15 and 16. N-11 comes with both strong denticals, and weak reverse denticals as the die wears. This looks like a late stge of N-11 shortly before the obv die cracked and formed the Cud found on "N-13". The pattern of the rev dentilation fading also matches a late stage N-11.
























