There was supposed to be an extra chapter 15.5 that explains why this is called chapter 15 and not 16, but guess we weren't fast enough with 2.
We changed the source and the new (official) one combined ch.10 and 11 since they were so short, so the numbering is one off from now on. Calling it 16 when it says 15 on the first page felt off so we went with this method. It’s essentially 16, so new and not the same again.