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.