So teachers re-use exams, but then, they usually collect all the questions back afterwards.
Really, it sounds like that IOS class is a joke, and they're (The school) just giving the grades away. As for your case, I don't see it as cheating at all, however my opinion matters less than your school's. Speak with the teacher, a teacher, or the guidance councellor, if they think this is cheating (when really it sounds like a lazy teacher) you might want to hold off then, but if they say its cool, then you're good to get a great mark, and a crappy education. However is it possible the teacher makes the test LOOK the same, but different enough so that you'd do badly if just memorized the results?
Back in my university days, it was standard practice to go to the library and get past exams from a certain subject (and prof) to study those to prepare for upcoming tests.
In fact for one course I remember NOT getting the past exams to study, and a few days before the exam in a special "Exam prep" class the teacher was offering, one student asked "Will looking at past exams help?" and the prof got a funny look on his face and said "Won't hurt". Then during the exam I noticed that on the top of the question page, the year was wrong, and realized he'd used an exam from 4 years previous, hadn't even changed the damned date (And I regretted not looking at that past exam).