Too much of a water change??

[iansfishy]

For the two years my tank has been running I have steadily done a 15 gallon water change every week of a total water volume of about 150+- gallons. Thats like, i dont know 45% a month (thanks grade 9 intro math, from 12 years ago!) After reading a diffrent thread on here, someone stated that even a 40% water change a month was extreme. Am I essentially stripping the water of nutrition?