If you bet on an under 1.5 market you are predicting that there will be less than 2 goals in the game. Your bet selection will win if there are 0 or 1 goals in the match. On the other hand, if you bet on over 1.5 markets then you are making a prediction that there will be 2 or more goals scored during the match.
In football betting, 'Over 2.5 Goals' is a type of market in which you bet on there being more than two goals scored during a match. For your bet to win, there needs to be at least three goals scored in the match. Two goals, one goal, or a nil-nil draw will be a loss.