As you get older, the feeling you get when you finally discover a chocolate egg is less exciting, I suppose. I don't really know. I'm only 13, still.

Welcome to growing up. Where the magic and wonder goes to die, along with a little part of your innocence 

Halloween used to be magical to me. Now it's like no one cares about it anymore. Christmas is still okay, though.

I think it's due to the fact that when you're older, you have more responsibilities to distract you. As a child, holidays take center stage because the only real thing you have to worry about is school. That's why everything seems to go by faster. Now you have a million different things to look forward (or not) to, and your mind can't focus on those holidays. Although seeing as how you're only 15, I doubt this is the case. (Unless you have a job already.)

That and as Tails said, adults tend not to treat holidays towards each other and teenagers like they do to children. Your parents hype up these holidays and give you all sorts of magical stories. But as you grow older, your friends (and parents' behavior) just kind of become apathetic to it all, which really dullens the enthusiasm. I think part of it has to do with the fact that as teenagers, they want to appear "cool" and grown up. Showing enthusiasm is not cool, and not grown up. A lot of society seems to be under the view that holidays are for children to enjoy only, and kind of force that joy out of you.