Bon soir roulishollandais,
I am not following this current AF447 discussion - just occasionally dipping in - and I certainly do not want to get involved in a latterday argument about Mont St. Odile and the ergonomics of the FPA/VS switching and displays on the original A320 FCU and FMAs. Suffice it to say that they were much improved by modifications resulting from the investigation into that accident, as I remember only too well.
But I think you might have another look at your sentence:
Flying at 220 Kts a 15% slope requests 3300 Ft/minute, as we pilots all know (220 x 15 = 3300).
I do not think so. You may remember that the rule of thumb for a 3-degree slope is that the required VS (in ft/min) is five times the groundspeed in knots. (I think most of us mentally divide the speed by ten, and then halve the answer to obtain the VS in hundreds of feet-per-minute.) At 220 kt that gives 1100 ft/min (add a tenth of that for a 3.3-deg slope.) Using the one-in-sixty "rule" (approximation), a 15-deg slope would demand about about five times as much, i.e., 5500 ft/min.**
** Non instrument-rated readers please note, the above are approximations only.