I think taking under 2.5 goals is a risky bet for that match. If Tottenham score an early goal the game will open up fast because United will have their backs against the wall and Mourinho will command more attacking play which will lead to even more opportunities for goals by both teams. I think this game could go either way easily and it will be over 2.5 goals. Just look at the results of the EPL games from yesterday.
Yesterday was very entertaining all matches got over 2.5 goals but today is a different day so don't compare it with previous result, but I also think so this game will go over 2.5 goals Manchester United is struggling so they will choose attacking style for this game to make secure 3 points, agreed with you over 2.5 goals.