Copied from another site:
Do not exceed the maximum working angles for the PTO shafts. The PTO drive should be disengaged when the joint angle exceeds 45 degrees or the joint angles are unequal. The maximum operating angle is 25 degrees. However for short periods at reduced output the maximum angle where contact between PTO drive shaft guard and rotating components is avoided is 45 degrees. When Stationary the max joint angle is 90 degrees. Aim for small identical joint angles when operating the machine. Wide angle PTO shafts have a maximum operating angle of 25 degrees. For short periods at reduced output they can be used up to 80 degrees. When stationary the maximum joint angle is also 80 degrees. Greater angles will result in premature wear and damage to the joint. When a wide angle joint is used on a PTO shaft the pivot between the tractor and implement must equal the pivot point of the wide angled joint. The single joint at the other end of the shaft has to run straight.
So then what is a "wide angle " joint?
Another site indicated 15 degrees, if you can, but say the life of the joints decreases with more angle, beyond one degree.
I see again, all things in life have a balance between options. I've been using an emergency generator off a 28 HP tractor at full 540 rpm and I'm sure the angle is over 15 degrees, yet no problem.
My measurement shows you at about 16 degrees now.