The fact that people have a "cache" of guns is one of the big problems. Why do people need 15-20 guns?
Well in handguns, everybody needs at least a couple of revolvers....maybe a .38 and .44 Magnum, and maybe a .22 for target practice. In semi-autos you need a couple of 9mm, a .45, a .380 to carry, and maybe a .40 if you can't decide between the 9 and the 45, and a .22 for target practice . That gets you up to about 9 handguns.
Throw in a couple of shotguns for home defense or hunting, a 12 gauge pump, maybe a 18.5 inch double barrel for the house.
If you hunt slightly bigger game, you may need a 30-06, a 30-30, a .270, .308....so figure at least 2 or 3 more rifles. If you are into varmint hunting, throw in a .223, 22-250, or the like. So, that's a couple more. You need at least one semi-auto .223/556 or 7.62x39 to protect yourself from SHTF scenarios. Maybe a longer range , harder hitting .308.
Then if you like to plink or squirrel hunt, and like .22s because they are cheap to shoot ( or used to be), you need a couple of bolt actions, at least one semi-auto, a lever action for the times when the cowboy comes out in you, and possibly a pump. So, there is a minimum of 5 .22's. Throw in the old .22's , etc passed down from your father and grandfather, and you are up to maybe 25......9 handguns, 2 shotguns, 5 centerfire rifles, 5 rimfire .22s, and whatever is passed down.