The original poster you quoted said his mortgage rate in 1990 was 15.4%. You said that was wrong. The link I posted shows he wasnt wrong.
You now say only new mortgages would pay that. The link I posted shows the rates as variable rates. So, no, not just new mortgages but those on variable rates also.
If you read the link fully, you'll see fixed rates were averaging over 13%. Well above your unsubstantiated figures.
Once again, the poster you quoted is correct. You are incorrect to question him/her. As my link proves.