As always, it all depends on the person.
If they dislike tickling, and REALLY dislike it, not "dislike it, but deep down inside love it" then it'd be torturous. Not real torture per se - I think, especially in todays wussy world, words need to be used to what they really mean....this coming from a guy who's a wuss! 🙂
Real torture is pulling out fingernails, made to eat shit, punched repeatedly in the face....and it all goes downhill from there.
If a prisoner had a choice between the above...and worse! or being tickled.....THEY'D ALL choose tickling, 100%. "Hi, you can either be tickled on your feet, even WITH pantyhose which makes it worse...OR, we can pull out your fingernails and then put you in a closed in, claustrophobic box for days on in where you'll have to shit and piss on yourself while having no food to eat....." Yeah, I think everyone would choose the tickling!
Of course, on the wussy torture line, yeah, it'd be funny to have two prisoners being tickled, one who hates it gives in after several minutes, and the other happens to be a tickle fetishist, and is like "Ha ha ha ha ha!!!, you'll need days before I'll talk!"
For me, it'd be like "You can tell us everything you know, or we can make you watch hours on end of Reality TV programing...first up, The Bachlorette, then, Big Brother Season 17..."
I'll be like, "I'll talk, I'll talk!!! I'll even tell you all of France's and Bolivia's secrets too!!!!!!!!!!!!!!!!!"