I have an obese client who I train twice per week for 30 min. sessions. Twice she has expressed to me that after our workouts she is so damn tired the rest of the day. We are only doing 30 mins and it consists of beginner exercises such as BW squat, res. band presses, & TRX rows. I review her food log weekly and her diet is very good, as well as her post-workout meal. I think a good part of it has to do with sleep issues.
what you are describing does not seem much but it is to her. I would replace some of the exercises with stretches but ask her to do some exercises at home so that the same workload can be spread out a bit.
I assume she is a beginning exerciser. It is sometimes really difficult to find the right entry level. What appears absolutely nothing to us is a real workout to others.