The initial 15° initial NU is not a command by the way, if you use derate plus ATM (and probably improved climb speed schedule as well) an initial pitch of around 12° is likely enough, more would lead to a speed drop. There is a reason why there is a Note in the FCM which says that the FD pitch command is not to be used for rotation.
To be honest, pitch in excess of 20° seems to be rare in the NG, slightly more common in the 700 than the 800. However it was quite common in the classic during initial climbout, up to 25° was considered perfectly normal.