Hello, welcome onbard and thx for your testimonial. In the sentence above, I guess you meant 1.5
M? Because a 1.5
k would give a pot value of 1.495k.
To change a 500k pot in a 400k one, it would require a 2M resistor.
Handy calculators can be found online BTW. Here is an example among others:
FWIW. HTH.