15 degrees allows a wicked sharp shaving edge, but is more fragile under anything but delicate to moderate use.
30 degrees can be made to shave, but not nearly so scary sharp. however, the edge will last longer under use, for hard use knives, outdoor knives, camp knives, etc.
My daily carry folders get between a 20 and 25 degree final edge, and that is a good compromise.
Machete's get 30 degrees.
15 degrees was just too fragile for me personally. I suppose on a self defense knife not used for much of anything else, this would be dandy IF you had a stoutly ground tip geometry to go along.
You will get as many opinions on this as there are a$$holes... everybody has one.