'Jelly' Bryce did fine with a 6 shot S&W .357 (and in MANY shootouts.)
Jim Cirillo did fine with a 6 shot .38 spl. many times (and also in MANY shootouts.)
Yet in the NYPD (same outfit Cirillo was with) they fired 50,60,70, and yes over 100 rounds at attackers, some of which were unarmed, and still didn't do well (and yes, reloaded in the process.)
In Dallas cops fired over 100 rounds at one guy and didn't seriously injure him.
As Fastbolt posted above, 'Being able to make accurate and effective hits on their attackers.' is what counts.
Simple as that.
So don't think your 15+ shooter will solver all your problems. In fact, they make make them worse if you rely on capacity and neglect to practice ALOT.
"The government has confiscated all of our rights and is selling them back to us in the form of permits."