There are quite a few possibilities as to why your brother is unable to sleep properly, so I'll go over the most likely causes.
- Is he tired when he goes to bed?
It's possible that your brother just isn't ready for bed yet. You could help by playing with him before bed or reading him a story. 2-year-olds have a LOT of energy, so trying to dissipate some of that might help. Establishing a bedtime routine might also help.
- Was he sleeping normally before?
If this is a new occurrence, it's possible that he's:
- Scared of the dark
- Not used to sleeping in a "big boy" bed/Not used to sleeping alone
- Experiencing nightmares for the first time
It could be one of the above, or all three. Dr. Marc Weissbluth has some more information about proper sleep habits and other probable causes for a change in sleep behavior. Based on what you've described, it sounds like he may have had a bad nightmare at one point, and is afraid of falling asleep (that "waking every 15 minutes") in fear that the nightmare will "get him". Alternatively, he's having very frequent and vivid nightmares when he falls asleep, enough to wake him up screaming and crying every time.
Try to communicate with your brother. Is he scared of something?
Regardless of cause, have a serious talk to your parents about this, especially if you think it's going to start negatively affecting your school performance.