AFAIK 15 AOE means a circle with a territory of 15.
That gives us 15=Pi*r^2 => r=sqrt(15/Pi)~=2.185
Assuming the circle is centered on the caster, that would make the spell affect anything withing a range of 2, or just a space of 1 between the caster and the affected enemy.
I'm not sure about wether it affects friends and foes or only the latter, since I haven't checked or tested those things, but atleast I can give you an approximation fo range
