After reading a few reviews and trying the demo I am really considering 15$ for an arcade game, but can someone tell me how many hours the average person might get out of this game because I will not pay 15 $ for 2 hours or less.

It's more than 2 hours. It's better than a lot of $60 games. Buy It.

You shouldn't think in terms of hours anyway; it's a bad mindset.

A lot if you don't use a guide.

It's not particularly long, but it's definitely worth the cash. Length all depends on how quickly your mind adapts to the time mechanics, and even then some of the puzzles are devious and will take a lot of work before the 'Eureka' moment.

BUY IT.  Don't give a fuck about the hours, as long as you don't cheat those will be some of your best hours of gaming in a while.

Personally I've started from scratch playing the game about 7 times, it's just a fun game to play, even if you remember the puzzles.

Yep as has been said without a guide the game is hard so pick it up.

I did it in a day without a guide. Today as a matter of fact! I was a latecomer to the game and I deliberately bodyswerved spoilers and I thoroughly enjoyed it.

Having said that, my first run through of portal was over in just under an hour as well so I guess I find puzzle games are my forte. Even still, like Steve_C was saying, it's a bad way to judge the game if you're doing it solely by hours -- the experience will stick with you for far longer than a long RPG or whatever.