+15 on top is an aweful lot, I have doubts about your engine holding a constant headspeed at +15? If it can, what fuel you runnin'
!
All kidding aside, I always start at center stick and work from there. Are you gonna continue to run +6 (hovering pitch) at center stick? What are you doing about your idle-up curves? I like the 0 degrees at center for all conditions method.
Either way, set your pitch curve back to the factory numbers (0,25,50,75,100). Now center the collective (throttle) stick and make all the servo arm/linkages 90 degrees. You've already had the heli setup, so you might not need to redo that unless you're gonna change to 0 deg at center stick. Next, fix your pitch gauge to a blade and adjust the pitch links to get the pitch you want at center. Now you can use your transmitter pitch curve to dial in the pitch you want at low stick and high stick. Next, fill in the remaining steps to make a linear curve.
For some reference, here's what I generally use for pitch settings in the various flight conditions:
Normal:
-3, -1.5, 0, +5.5, +11
Idle-up 1:
-11, -5.5, 0, +5.5, +11
Idle-up 2:
same as idle-up 1
Throttle Hold:
-4, -2, 0, 6, 12 (or a little more depending on the model)
These settings will have you hovering about 3/4 stick (depending on headspeed, blade length, etc.) and you will be able to switch between modes anywhere above half stick w/o jumping (if your headspeed settings are the same for each mode).
Hope some of this is useful.
Ben