Typical academic leave notice period?
It seems to me that for a position with teaching duties, the main question is: leaving during the year versus leaving at the end of the year. Suppose you teach a semester course and you give your notice in the first month, then 3 months sounds a bit short. It might be that they want to make the schedule for the next year 3 months before classes start and want to know what teacher are still there next year.
My advice would be to discuss this with the university. However if you are looking for a job that you can quit at an arbitrary time within weeks/a few months, then teaching might not be for you.