Redirect to the next page after downtime

Good morning! Home I'm creating a rating system, it's choose the option , the user is redirecting to another page to leave a comment , and followed > show another page to thank , and everything back to the beginning. Home But there are users who only choose the option and leave and remains the comment page ...
What I wanted to do is, for example, after 15 seconds (for example) if there is no movement, the page automatically recognizes the comment, validates only as an empty comment, and goes to the " thanks ", otherwise from the beginning if the user is writing it can take as long as you want. Home I've seen several similar topics but it was with sessions , to disengage the user, and I'm not using any session ! Thank you!