After you have practiced and learned to stay focused and gotten skilled at studying for 15 minutes at a time, you will be ready to start studying for 60- minutes at a time.
Remember, you might have to practice a lot before sitting down in your sacred environment and studying for 60 minutes, so keep practicing until you can.
Also, remember, when you take a break every 15 minutes, it is important that you get up, get out of your chair, and move around for 5 minutes.
If you’re part of an athletic team, an excellent thing for you to do is 15 push-ups or 25 situps; this will get your heart beating and send more blood filled with oxygen to your brain which will keep you more alert for your next study session.