Rick - Cool.
It seems that you are getting the important message across - ascend slowly to the surface.
I also come from learning to dive back when the rule was "as fast as your smallest bubbles, and get the hell out of deep water" Which I was taught, and I accepted as recieved wisdom from an instructor repeating current agency dogma.
It's only recently, when I actually started to think about what I was doing (ie once I got over the belief that I was immortal, and could not be narced or bent) that I realised the importance of slowing the ascent near the surface. (I was also playing with calculating the integral of pressure over depth giving the same ideas as you expressed)
Strangely enough, I began feeling a lot better after dives with the slow ascents... even managing to stay awake. Even though I was doing deeper and longer dives.
However - I still think the idea of neutral at 15 fsw is plain dumb, even given your convoluted definition of neutral.
IMH(I try to be)O
Neutral implies that as you breath in, you ascend, as you breath out, you descend. That goes as far back as PADI 101 and fin pivots.
If you are stationary in the water column with a full breath, you are not neutral, you are negative, and compensating for it using your lungs as boyancy control.
So to teach this 'neutral at 15 fsw' nonsense, you are also trying to teach your students that neutral means with 1/2 full lungs at depth, but at 15 fsw it means lungs full?
How about taking the simple, straightforward approach, and teaching to be neutral at the surface? (which is essentially what you are doing anyway, you are just confusing the issue with this whole neutral with full lungs at 15 fsw malarky)
Mike