I need some good book series recommendations!?

I'm 15 too. Here are my recommendations. You should for sure read Harry Potter, but maybe try some Stephen King books. He doesn't do that many series' but he does do some really good short horror story collections. Some of my favorites are the Skeleton Crew, Night Shift, Full Dark No Stars, Hearts in Atlantis, and Nightmares and Dreamscapes. As for series, try the Bachman Books, and the Dark Tower series. Some of his better single books are Desperation, IT, the Shining, the Running Man, the Dark Half, the Mist, Misery, and Firestarter. Although, all his books are rather long, and can be disturbing. I don't find them scary, but I know some people who do.