Error code 15 is associated with an operation being aborted, and, in my experience, is usually associated with either making or clearing selections while the engine is still performing another task which the engine has to run again when selections change. It has never actually negatively effected my app, and as long as you are not experiencing any unexpected behavior from it, which I'm assuming you're not, it's probably safe to ignore.
The 'Operation aborted' happens when the user makes (or clears) a selection at the same time we are trying to fetch data. The client code should try again and get new data that reflects the new selection state. So this error is normal, I don't really know why we print it in the console, we probably shouldn't.
I have updated the link, it should work now.
Erik Wetterberg https://extendingqlik.upper88.com/