I'd love to be bendy enough to work my way through the ashtanga primary series. I have just restarted ashtanga at my gym, it's a one hour class and by the end I'm absolute exhausted so I'm sure I wouldn't manage 2 hours!
I thought I wouldn't get through it but actually the last hour is floor exercises.
I found using blocks really helpful in getting hips into the correct position.
Some of the standing exercises where you raise your knee and hook onto your toes before stretching your leg out to the side - that was a challenge too far. I just stood on one leg grasping my knee and trying not to fall over!
Some of the others in the class are amazing - I watched a fairly chunky grey haired gentleman do an effortless headstand!