I agree the 4% rule is too aggressive nowadays. But every .25% increment lower means a huge improvement in sustainability, so even adjusting down to 3% is profoundly more conservative than the original rule. At 1.5% you are going lower even than endowment funds aiming for perpetual maintenance of principal (they often use 2%-2.5%).
The 4% rule of thumb was calculated to minimize risk of running out of money during the time period. 1.5% * 30 years = 45%, so an investment that simply keeps up with inflation would leave you with more than half your cash after 30 years.
And note that the stock market almost always has positive real returns over periods as long as 30 years (see William Bernstein’s book Deep Risk), so the assumption “just keeps up with inflation” is already very pessimistic.
The 4% rule of thumb was calculated to minimize risk of running out of money during the time period. 1.5% * 30 years = 45%, so an investment that simply keeps up with inflation would leave you with more than half your cash after 30 years.
And note that the stock market almost always has positive real returns over periods as long as 30 years (see William Bernstein’s book Deep Risk), so the assumption “just keeps up with inflation” is already very pessimistic.