According to standard firecalc, assuming default values of 75% stock weighting and 0.18% investment expense ratio, a 4% withdrawal rate would last 30 years about 94% of the time. Bumping your withdrawal rate up to 5% occasionally would make the success rate drop. How much it would drop would depend on the timing and frequency of the 5% withdrawals.
The previous paragraph assumes, though, that you're talking about taking 4% of your $1.5M the first year, then increasing that withdrawal amount by inflation for subsequent years. If you're talking about taking 4% or 5% of your portfolio value every year, then you will never go broke but your annual budget will vary wildly and may get very small (like 4 or 5 cents if your portfolio drops in value to $1.00).
2Cor521