I think getting hung up on the 15kg/15% doesn't make sense. That's just the average for the subjects.
The following article by Richard Doughty illustrates it's a very personal thing indeed:
https://www.theguardian.com/lifeandstyle/2013/may/12/type-2-diabetes-diet-cure
Absolutely.
I'm surprised this video on YouTube hasn't got more views, since diabetes is such a common thing these days! Maybe it's because the video just shows slides while the audio plays a presentation by Roy Taylor. Maybe dancing cats would give it more views!?
Anyway re weight loss and whether percentage or absolute values are important, neither seem to be anything more than statistics which just show that: it's probably worth trying to lose weight for anyone who can safely afford to, because it stands a good chance of improving your insulin response. If you keep losing weight you may get lucky and have a very dramatically improved insulin response at some point.
So you could look at the first Newcastle study and get hooked on 15%.
Or you could look at the inspiration for the Newcastle study, which is the surprising remission rates after bariatric surgery. That will give a very different statistic: bariatric patients showed the biggest chance of remission at 20-30% weight loss. And bear in mind that these are likely to be very heavy people, so in absolute terms that's a heck of a lot of kilogrammes.
Not everyone can afford to lose 30% body weight, so that's another reason not to get hung up on the stats. The Richard Doughty article is a great example of the fact that even you are fairly thin and active, it's still worth trying, again so long as it's safe, e.g. you don't get unhealthily thin.
Video here, I'd say it's worth putting the kettle on and sitting through it all if people haven't already, but if you just want to see the stats Roy Taylor shows for bariatric patients, skip to 36:30.