Why should an AR-15 not be available to the general public? You're making some blind statements here without a shred of anything to support what you're saying. What's so bad about an AR-15 that doesn't apply to a whole host of other weapons?
Limiting magazine size will achieve more or less nothing. Firstly criminals will simply keep their existing large capacity magazines, and secondly if you have any idea how fast you can reload a semi-automatic magazine you'd know that limiting the magazine size simply means your would-be killer needs a bunch more magazines (you can buy them over the counter at sports stores and if you're not planning to survive your attack you won't care if you run up a huge credit card bill buying them. We've all seen the likes of Keanu Reeves reloading his gun in the movies and, if anything, it's slowed down for artistic effect. When I was out shooting with a couple of friends in the US I was curious to see how fast I could reload, based on virtually no prior experience, and within a couple of magazines I could reload as fast as they do in the movies. I'm reliably informed that more serious shooters can reload so fast that if you were measuring the time between shots you'd struggle to tell which shots had the reload in between.
The type of weapons people can own is already limited. You can't buy a fully automatic weapon without additional licensing and even then they are hideously expensive. A friend of a friend has a fully automatic rifle, with appropriate licensing, and reckoned it was worth somewhere north of $10,000. If you want to argue that the types of weapon that people can own should be limited how about coming up with some concrete suggestions for what should be banned, why it should be banned, and how to objectively differentiate between an acceptable and an unacceptable weapon. Otherwise all you have is the typical bleating about "assault weapons" without even the faintest hint of what defines an "assault weapon".