You'll have to go through immigration in Munich. ("Customs" is a 10 second walk exciting out of baggage claim for most people who have nothing to declare.) If your incoming flight is on time, 2:15 should be plenty of time. If you are late, then you would automatically get put on the next flight to Dresden, assuming there is one. (Assuming your two flights are both on one ticket.) When I make connections like this, I always check that. It wouldn't be unheard of for a flight from SFO to be two hours late to Europe, even if unlikely.