I expect a lot of people have low LTV these days due to the huge gains they've made on their properties, so it might be less than a 1.5% markup. Unlike 15 years ago there should be fewer plunged into negative equity and hence unable to remortgage away from SVR.
I'd be surprised if there was a sustained period of 9%. Right now, interest rates have needed to rise to combat inflation but inflation is likely to tail off simply because it's an annual rate of change and the price rises of a year ago start falling off the charts.
With rates at 4% now presuambly the '+3% affordability stress test' or whatever it's called should be checking if people taking out new mortgages could handle a 7% base rate.
Unemployment remains low, to me it looks more like a 2008 situation than early 90s, and it was the latter not the former that was bad for repossessions (repossessions per year didn't even hit 50k in the last 'crash').