I've seen secondary throttle plates stuck open before. That drops your vacuum.
So which is it? 12 or 15 initial. Accuracy is the key. That's why you confirm your timing tab with a piston stop.
http://www.crankshaftcoalition.com/w...op_dead_center
Some cams were ground advanced or retarded 4-6 degrees.
If you had any fuel leaking it would speed up your idle. Likely not a problem right now.
Can you screw either mix screw in all the way without the motor stumbling and wanting to quit?
Where's your vac advance hooked to?