As a rough guideline, it does all right to say when you can say for sure, but in this case, as the book was published 2 years ago, its definitely not public domain. Perhaps in a number of years from now, once there has actually been enough time for more books than the ones which went public domain back in The Day, to go public domain, I would be giving a more thorough answer. AND assuming it isn't extended again.
I suppose I could go into a 2-page lecture on all the ins and outs, but the end result is basically the same. If it wasn't written before 1923, is it public domain? Most likely not.
Was it written within the last 3 years? Yes? Oh, then definitely not.