It is not 15 deg of bank, it is track.
Making the difference between SID design and the way you fly them wont change the fact that you may need to turn below 400', which will be always a maximum of 15 deg compared to rwy hdg, it is not considered as turning.
This would be still considered a straight SID (no turns).
More than that can only be at or above 394' on any IFR SID. That would be a turning SID.
That is the way I see it with the info I have, and that is the way I always have seen it done by pilots I flew with.
In any case, if somebody knows more about it please share with the rest, if possible explaining where we can find a reference
