Yes. "Age grading" overrates young teen phenoms cf. Ping sisters. The good news is that Tuohy is now very good at 20, so we can mostly forget what she did at 15-16. We can be optimistic that she will further improve but still not sure if this will be "only" very good or reaching world class. Cf. Mary Cain and Alexa Efraimson who were still contenders at 20-21 (Efraimson even longer) but never beat their under 20 marks.
What is known about her mileage? Has she done altitude training camps? Tuohy has obviously been training on a very high level for around 5 years already, so it's not clear if such fast improvements are to be expected like in cases of low mileage teenagers who then crank up mileage and get much better suddenly, especially over longer distances.
It seems also people are making too much of these XC results. Tuohy is fast enough in the 1500 to run sub 15 (I think she is much closer to this than Valby) but again, she is not a 800/1500m runner recently gone up in distance and ran an extraordinary 5000m at not quite 16. Not saying she cannot make a big step indoors or next spring but I don't really see why such an experienced runner at the distances should have run way below potential in the last summer, i.e. that she was closer to 15:05 shape than the 15:14 she actually ran. Unless there were always horrible conditions or a huge negative split.