With a true Keynesian model, we would have employed more people in the public sector, e.g. to build cheap, good rental homes for anyone who needed one. Then people would not have had to borrow for an apartment unnecessarily.
On the one hand, this would have reduced the people's indebtedness in the first place. When everyone who wanted it could get a good, cheap rental property, this would have reduced housing speculation and lowered the prices of privately owned housing in general. Then those who still wanted to buy a home would not have had to pay and take on so much debt. When people paid lower rents and lower interest rates, they would have been able to consume more and maintain consumption.