Thc bonds temporarily to the fat cells in your body, that includes the brain. Not sure that cannabis is the best medicine for a developing 15 years olds brain specially one in high school. The effect of thc bonding to the brains fat cells is only temporary but it makes it harder(not impossible)to retain learned information. Might see a drop in test scores.There are several studies confirming this. In the end you are the parent do the research,and do what you think is best.