Earlier (a few years ago) the interest rate of the Hive Dollars (HBD) savings was 20% APR.
Some of the witnesses wrote that both percentages are sustainable for long term.
I can only hope that the interest rate of the Hive Dollars (HBD) savings will remain in this range (between 15% APR and 20% APR) for long term (for years, for decades).
Inspired by your post I summarized my understanding of HBD in a separate one, would be great to get your feedback:
https://ecency.com/hive-167922/@dankorox/money-aka-hbd-bgf
I am also not a Hive blockchain expert, nor a financial expert/advisor (so this post is not a financial advice, only my personal investing decision, my personal investing approach, and my personal experience), but I wrote a short comment under your post.