I own a PSP but not a DS. I have seen people play the DS. I can say that the PSP and the DS is like the PS2 and the Gamecube or the PS3 and the Wii. The Nintendo systems are more for younger people with the games they make and their overall image. I think the PSP is too fancy and more expensive. 15 is a tough age, you want to get the PSP if you want to seem more mature and if you like the more mature games or you get the DS if you like cartoonish mario type of games. However, both systems have a variety of games so it's not completely either or.

My teens have the psp and they absolutely love it. They can get on the internet with it also.

I've had a psp, and I did like it cause I could use it online. but that was the only good thing about it for me!

for a 15 year old i would say a psp. the ds is fun but a psp has more mature games that a teenager would like