How would three level tens fare against a CR 14 False Hydra

I’m currently writing a one-shot adventure to run with my friends that has a false hydra as the final boss. I found the stat sheet for it here https://www.gmbinder.com/share/-LAoJ_bfNWBTTmIV9KQ_ I’m planning on using the adult form with only three heads. Do you think that this thing is beatable with this party? Or will I need to bump it down a notch?