My strange habits

I am a full time student, and work 20+ hours a week so I don't have time to spend running or weight lifting. So I have resorted to doing 100% body weight exercises in my room in the evenings. I even have a pull up bar attached to my bathroom door frame.

Here is my question. When I work out, it is usually for like 15 minutes, but I really push my self to do as much as possible. I go from one exercise to another and don't rest in between. When I am done I am very exhausted...

Is this really bad? I want to lose a little bit of body fat and get a better figure with a little bit of muscle just from body weight workouts. Do I HAVE to spend like an hour to achieve this? Or will my 15 minute extreme killer workout be good enough? I'm too lazy to spend a lot of time on it...