A life worth living? What, so he can come back and still be a racist shitbag? Except next time he will make sure to not get caught? Realistically he's going to be released from prison even earlier for good boy behavior and then he'll get right back where he was: a racist shitbag.
He didn't go out and like, shout racial slurs to a bunch of people. Then I'd agree, 15 years is too much.
He fucking threatened to fucking kill and fucking brandished a fucking firearm at kids who were having a birthday party. Even if you remove the racial aspect to what happened, this shows a level of sociopathy, psychopathy that no amount of jail time will solve. Then you factor in the racial hate aspect. You don't reform from that.
The only solution for people like that, is to remove them from society indefinitely or until they're rendered harmless.
First, I'm not american but ok.
Second, I don't believe all criminals are irredeemable.
This special kind of shitbag though? No way he will change. The only cure for this level of shitbaggery is a bullet in the head. However, since we've moved on from summary executions, the next best thing is locking them away until they die.
Here's facts: I live in a country where drug dealers get like 2-5 years tops, and are often released early on basis of being good little boys because prisons are overcrowded. They don't reform, they don't change, they just go back to dealing drugs. For some of them it's even something to be proud of.
There's things you simply don't reform from. Brandishing a firearm at kids having a birthday party, and threatening to kill them is one of these things. A normal, functional person with a normal, functional brain doesn't do that. And, again, that's even without factoring in the racial aspect, which makes things even worse.
These people are net losses for society. The only thing they will learn from a short sentence is that next time, they'll cover their tracks better. They won't be less racist. They won't be functioning members of society. The only thing a short sentence achieves is, I believe, in the USA you can't legally own a firearm if convicted? Like that would make them less useless racists pieces of shit?
Maybe pick a view that is rooted in reality.