Is it all on LH, or AF? Either terminal for Schengen departures are fairly easy, and I would say that arriving back at 13:45 would be plenty of time. As long as you are already checked in and have your boarding pass, you should be fine. Aside from the long walks, MUC is a very user-friendly airport. If you are flying on AF, you depart from T1, which is older, and if you are on LH, it will be from T2, the nicer Star Alliance terminal. If you don't feel like cutting it close, there is a Hofbrauhaus restaurant on the second floor of T2, and a nice biergarten called Airbrau in the atrium between the terminals.