Depends upon your choke and barrel length, but at 15 feet, your normal hunting type shotgun will have that much of a pattern - choke is much more of a factor further out at the range you would be aiming at birds on the wing.
One reason sawed-off shotguns are illegal is because they have a larger pattern at close range.
One reason sawed-off shotguns are illegal is because they have a larger pattern at close range.
No, shotguns with barrels less than 18” are restricted because an anti-gunner came up with the “evil street-sweeper” image and it was politically viable.
If a 40” minimum that made your shotgun 20 lbs. and completely useless for defense were possible, they would’ve gone with that. The pattern from a 12.5” or 14” barrel is still very tight at close ranges...but it would be lighter and much more maneuverable for a lot of residents so it’s just another way to harass people and make defending themselves more difficult.
For an 18” defense shotgun, completely open choke, a decent rule of thumb is an inch per yard. So you’re not going to just let loose and paint whatever wall your attacker is near...or even throw a torso-sized spread. If you point at center mass most of your shot will fit between two of his shirt buttons (well ok an area that size on his XXXL).
Think of a shotgun at any defensive range as a fist of lead.