I just measured my wingspan, fingertip to fingertip laying on the floor and got 78 inches. measured fist to corner of my mouth. and got 32... Do they even make them that long?
78-15 equals 63 63 divided by 2 equals 31.5 AMO drawlength. 31.5 AMO would be a good starting point for your draw length, provided your 78 inch wing span is correct.