I just have to know that you can write decent code. I don't want to waste my time or yours if your code in the language we need is not up to a minimum standard. When I have to train a new candidate on a million line code base, I cannot afford to spend time also training them to be competent in the native language of that code base.
This is not about "coding passion" or notches on some Github post...this is about whether you can do the job. Although one advantage to a Github profile is I can look at your repos and see whether you understand the basics of using git as well (yet another requirement of the position).
I, for one, think your 15 hours was well-invested.
I think this is a good piece of advice here, no need to call other people dumb and lazy.
Inventing a project interesting enough to focus on for 15 hours can be difficult. Just like learning SQL without a dataset.
Inventing a project also isn't likely what you want to be hired for, so it's reasonable to have that low on your priority list.
Free software is constantly filling the gaps that I would want to create a "side-project" to fill. I'm not saying it's particularly difficult to find something to work on, but it certainly isn't trivial.
Because of this, I at one point spent maybe about 15 hours putting together a small project specifically to use as a code sample. This code sample, which again took maybe about 15 hours to put together, served its purpose for years.
To avoid this tiny amount of easy work that has such a high potential upside is, to be frank, just dumb and lazy.