FWIW, this bundle with all 17 books can be had for $18, which I'm guessing is less than the cost of a printed copy of any one of the books.
However I've bought book bundles every year for the past 8 years. In 2018, a full bundle was usually $15, with a suggested price of $25. Starting in 2021, the bundles were bumped up to $18, still suggested at $25 (but O'Reilly bundles cost more).
15+3 is a 20% increase, but is still below retailer's $20 threshold "impulse buy" rule of thumb.