If I am doing a SIP roof with a pitch of over 12/12 the length of the panels will be about 15' 6". Do I need framing Under the 12 1/4" OSB panels or can I embed the framing in the panel itself? I would rather put my framing inside the panel but you got to do what you got to do.

You should use an i joist 11 7/8 high at 24'' distance center to center will be enough for 50 pound live load, 9 1/2 inches high would be enough up to 20 feet but your panel is too thick, you can verify with any i joist manufacturer, it is one of our product.

Pierre Desjardins
Banerpan

Rsipgeo,
What is your location? Your snow load requirements would be the only limiting factor.
If your panels are only 15'6", then the horizontal span cannot be much over 10 feet.
With 12.25" panels, you will be using 2x12 (or eq.) splines. A single spline 4' on center, should be more than adequate for most locations.