Not only what he said, but, by using less than lethal ammo in a lethal weapon, aren't you admitting that you didn't fear for your life enough to employ deadly force? Is that a warning shot?

I have been taught, in roughly 100 hours of self defense firearm training, that warning shots indicate a lack of fear for one's life and should never be used under any circumstances. As much as I hate to say it, especially with the current climate regarding guns in this country, if you feel threatened enough to deploy a firearm, you better be ready to totally neutralize the threat with as few rounds as possible. Preferably using ammo that some LE agencies use to avoid the killer bullet offense.

The OP's original question was about using the 15-22 for HD. Is it the ideal round? Absolutely not. Is it better than a box of rocks, or a stern voice? Absolutely! Not everyone can afford several purpose oriented firearms, and need make do with what they have. I applaud the OP for trying to get good info to base his decision on, it is the responsible thing to do. And since he now says that SD training is in his future, I am sure all will be well at his home.
RichH