Weird. I wonder why it's working for me but not you. Tried in browser on laptop and in phone and it gives the correct reponse

Because you're typing in "was 2015 10 years ago", whereas I'm typing in "was 2010 15 years ago".

Mild dyslexia strikes again! Strange how it gets that right but not yours though.

It doesn’t understand the question. It just generates probabilistic content based on your prompt. No math was actually attempted by the computer (which is the craziest part of all!)