Roald Dahl is a great example of a prolific author who would write perhaps 4 hours a day and would spend the rest of his time drinking, relaxing, and tending to his farm. As far as I know, a casual pace like that is pretty common among writers - though maybe not to that extreme.

Slogging through 15 years of practice every day is a technical endeavor. If you need to learn how to do something or to master a technical skill, then yes, volume of work will get you there. Code is a tool that is used to create, and I think the quote you selected just serves to underline the difference between learning how to be an effective engineer vs learning how to become an effective technician.

Edit: constant practice is definitely important, but relentlessly working is not.