If you are able to develop insight into your breathing for 15 minutes, then you can focus your attention on other areas as well. Start with the body at first.
Awareness Expands Over The Body
The first exercise for gaining insight is to allow the awareness to expand from its point of focus, at the nostrils or abdomen until it covers the whole body.
This can be mastered with regular practice.
Don't go too fast. If your point of focus is the nostrils, then allow your awareness to become aware of the face, then let it further down to the neck, chest and then to the abdomen.
Try to feel the body both from the inside (the sense of being in the body) and from the outside (the sense of being in contact with whatever is outside the body). Then as your overall awareness develops, you will have the feeling of a unified whole body rather than some physical parts held together.
Awareness Sweeps Over The Body
The second exercise for gaining insight into the body, is to allow awareness to sweep the body, slowly and in minute details, again trying to feel both from the inside and the outside.
Start by directing your awareness to the top of your head. Don't worry if you don't feel any normal sensations of the body. You can feel them if you can increase awareness of your body.
Irrespective to these sensations, let the awareness travel down over the face, neck, shoulders, arms and into your hands. Feel the awareness of what the hand is resting against. Finally sweep the awareness to the rest of the body that includes the back, abdomen, the buttocks resting on the cushion, genitals, thighs, legs and feet. Sometimes you may experience pain or aches. Investigate it first and then relax into it. This will help you to take control over pain and stop it filling your mind.