I'm 21 now. Just finished college, and am ambling towards actual adulthood. Let me get myself into 15 year-old flac mode:

Alright, we're in there.

Here is my advice to you (and yes, the irony of giving advice about being yourself is not lost on me):

In 2 years, you have the option of nuking your entire social life once you leave school (I talk to exactly 2 people I knew in high school - one of them is the girl I've been dating since I was 16, the other is my oldest friend). Odds are very high that nobody but you will really remember what you did in high school a few years from now. You will be in college, if that is the path you choose, or really doing any number of things that interest you - you get to make actually large choices. But right now, you are kind of on a set track. It's not fun, but you are. You are right in thinking that ACADEMICALLY these years are purgatory - and it is also easy to view your whole life as school-based right now - that is more or less the message that you are probably receiving from every single authority figure in your life.

To the world at large, these years are utterly inconsequential. They are just the time between you being a kid and you being a working, capable adult. But they mean the world to you, now and for your future.

And you know what I would not have done a goddamn second more of? Studying. My little baby heart is breaking when you say you don't want to waste your time - THIS IS LITERALLY THE BEST TIME IN YOUR LIFE TO WASTE YOUR TIME.

And more importantly, this is the best time in your life to make mistakes.

Anything short of murder or pregnancy will almost definitely be forgotten by everyone but you in a year or two.

Your mind, body, and soul are basically rubber right now. Break some hearts, get yours broken - find what you want out of a relationship, or if you even want one at all (hint: they aren't actually as important as everyone makes them seem). Start a shitty band with your friends. Don't know an instrument? Learn one. You don't have to be good - you'll probably never play a show. Dream big, and do things outside of your skill level. Don't know how to make a movie? Sounds like it's time to make a shitty short film with your friends. Don't know how to code? Tell a girl/boy that you are crushing on that you do, and learn how to do it to cover your ass.

And I know I am stating most of this in terms of things you can do with other people - some of my best memories with some of my best friends are from stupid projects we spent too much time working on and never even finished - but you can do SO FUCKING MUCH on your own right now too. Get a shitty job as a dishwasher or cashier (which, by the way, is one of the few things I think you should ABSOLUTELY do if you have the time. Having a shitty minimum-wage job is an actually essential experience for growing up) to pay for whatever new hobby you have an interest in. Mine bought (cheap-ass) audio equipment and darkroom supplies; what would YOU spend $100 on if you had it? What are your passions? What are some small things you wish you knew how to do? You can learn virtually ANYTHING for free - YouTube is a beautiful, beautiful thing.

Want to know how I spent every second of my free alone time in high school? On the family computer, with a RockBand (yep, the video game) usb microphone and Audacity, covering my favorite songs. I never looked up how to do anything, I never looked at a manual, I just fucked around for hours and days and years. And it was all just for me - nobody else ever even heard them. And now I'm still fucking doing it, albeit marginally better.

If you had no college to worry about, no school to worry about, nobody to tell you exactly what to do with your time, what would you be doing?

Your teenage years are not for building a resume, they are not for building a portfolio, and they are not for building a future. They are for figuring out what kind of you you like.

So the question is: how do you want to waste your time?

EDIT: My sister is roughly your age right now, and these are conversations I've had with her too. Everything you're feeling is totally natural, and probably something your peers are feeling too. You're not alone in thinking that there is a right/wrong way to be a teenager (but there isn't, so don't worry).