That yield was also manipulated up to 12% from literally 0% in the early days.
I also didn't agree with it being lowered... especially at the bottom, but on-chain metrics suggest that 15% is working pretty well, and 15% is still a good deal and totally worth it.

The yield is whatever witnesses say it is.
Those are the terms we have agreed to as a network.
It's actually an old system that's been in play since Dan wrote the code.
We only just now started using it.