Arguably (though not certainly) a better punishment than death, which would have been a frequent consequence in most of human history for taking the lives of others (plural). Life imprisonment is simply an alternative to the state killing you.

You can die (so we don’t have to worry about your exposure to society) or you can stay in this institution (so we don’t have to worry about you). What do you prefer? ..aaand arguably you can revisit the decision on your own accord later if you choose the latter.

“Time head all wounds” refers to the lessening sense of gravity of experiences over time. This is a function of memory and the healing power of forgetfulness. Life sentences are therefore liable to re-evaluation and pity by their nature, whereas if death was meted out as the sentence, that too would be forgotten in time. I find that interesting, and perhaps it says that we should not trust such emotions in either direction (for or against a punishment) when figuring out how to manage people who systemically murder others.

It’s definitely pretty hard to determine how long someone should be punished for multiple murder. I expect the most capable would be the judge and jury, so it’s hard to improve on that decades later with minimal information.

So life for multiple murder by a 15 year old doesn’t strike up my curiosity for optimizing the sentencing. Unless there’s lots more info. This article didn’t provide any and since the journalist would likely research to make a good article, I expect there’s not any compelling narrative.