A Kel-Tec Sub 2K isn't going to do you much good at 16" -- it's only 16" if you have it folded in half for storage or transport. Unfolded and ready for use, it's a hair more than 29" --the same length as a pistol grip Mossberg 12 or 20 gauge -- and only a few inches shorter than an M1 Carbine. Don't know how long an M1 w/Paratrooper stock is, but is probably shorter than the Kel-Tec. An underfolded stock AK is definitely shorter than a Sub-2K.
If you want short, then why use a 9mm Sub 2K in the first place? Just use a pistol.
If you want "oomph", then a shotgun will do you better than the Sub 2K. If you want capacity or maneuverability (assuming 8 rounds of 12 gauge won't solve the problem), then consider a pistol.
True, the ballistics of a Sub 2K with a 16" barrel reach the optimum for a 9mm round -- but still far way short of a shotgun. The increased sight radius is a plus for longer distances -- but is moot for home defense ranges.
Again, i'm not knocking the Sub 2K (even though the magazines tend to fall out very easily) -- it's fun to plink with. But, I don't think it's the best tool for home defense.
You can't aim a shotgun that doesn't have a stock, and it's real hard to do with a folded rifle. You want a stock.
The Sub2000 is going to be easier to aim under stress than a handgun. Handguns are the hardest type of modern firearm to operate under stress.