I myself have just finished a month and a half of 19 classes per week. It was very challenging….but do-able. I wouldnt want to live with that as my regular schedule…but it is possible to do it. I agree with all the other answers here…it really depends on the intensity of the workouts. It also depends on the variety. I wouldnt want to be in a class with an instructor who has taught and participated in say 15 cycle workouts….or 15 weight classes…but mixed up to different classes and intensities…that would be a different story. It really does depend on your instructor and the intensity they are able to handle…the real question would be…are the 10th to 15th classes still the same quality as the first 5 classes? If they are still quality classes…then the problem doesnt really exist. Your instructor has found a way to co-exist and teach without burning out. For this…you should be happy!! Your concern for your instructor is appreciated by her I am sure.