30 minutes of warm ups sounds very long, even for a two hour class. Personally, I'd rather have a two minute warm up, then 28 minutes of strength and conditioning training.
To be clear, a warm up is a routine used to prepare the body for work. Generally, this is done by increasing the body temperature with full body movements. This should not be a terribly difficult task, it should be something the individual can do. (For example, jogging or jumping rope)
For strength and conditioning training, I'm referring to a routine where some facet of athleticism would be increased. This will be a challenging activity, and it might be such that is the individual struggles to complete it. (Body weight exercises --- push ups, squats, yoga, pilates; Anaerobic/Aerobic conditioning --- high intensity intervals, etc....)
That's just my personal opinion. YMMV.