Haven't really followed the public pension topic for quite some time, but just looking at a few things now i found this from 2017 that was interesting for those who want to know what some of those pensions are worth or at least how they're calculated.
And this which actually notes a 12.5 percent return (2017), so 15 percent isn't crazy high after all. And it shows the average pensions. Interesting stuff.
However - it does appear there is an unfunded liability. Sort of.
It notes that the total pensionable obligation is 276 billion, while invested assets are about 136 billion. Now - they're not paying out all those pensions, that will include pension money accrued by currently working members who will get their pension down the road but who are contributing right now. And it doesn't take into account all the interest that investment will earn between now and when all those pensions are paid out. So there is no real reason to believe that public money will need to top up the pensions - BUT... it is possible. Theoretically at least. Doesn't seem very likely at the moment.