Am I too young to think about if i'll have a spouse and when?

Yes, you are too young to think about that now.

well... as someone with 22 and who never had a girlfriend... or had sex... or kiss another human... i'm not the one to give you advise...
but yes, you are too young. for like, everything. or go and marry, out there must be some state that allowed a 15 years old human to marry, you are probably going to regret it in a few months, buy hey you could even be happy, who knows!

In the western world, 15 is probably too young to need to think about that.

Yes, you are too young to think about it.
Although it's quite normal. People tend to think. And over-think too. Unless you're in danger. Then people focus on surviving.
So... congratulations! It's not like there's a hungry tiger running after you.
And back to your love life... (or absence of it, by the time being) I am going to say my two bits about it.
Relax, you don't have to make NOW plans for the rest of your life. After all, you're just 15. How long do you want to live? Up to your 40s? 50s? 80s? And aren't you still learning things? Like in school? Is it the moment when you're best prepared to make your long-term life decisions?
My advice?
Keep going with your life. Study, fun, girlfriends... At some point you'll have a girlfriend that means a lot to you. Then you'll be thinking about marrying HER. (not just MARRYING, like wanting to marry without having someone in your life) And truth be told, maybe you'll marry her, maybe not. Maybe you'll keep going with your life after your "great love" and guess what? Probably you'll fall in love again sometime later.
So don't worry. You're too young to think about marrying. But it's completely normal to think about it. Welcome to the paradoxical human race. XD

No, not you're not to young to think about your future. So many people don't think at all and then suddenly end up being 40 with no spouse or kids wondering what the hell they did with their life. And then panic and marry the first moneydigger that comes around :D

I was 19 before I met my wife, Proposed on my 21st birthday at my party/ Now we've been together for nearly 9 years, married for 5 and just had a beautiful daughter (2 weeks ago). I definitely didn't think about it at all when I was 15, I tell you that much.

Well, you can plan things. But knowing that they never happen as planned makes it a lot easier. While it's good to have some objectives, to drive you, it's better to not overthink it.
Like Capile2 said, don't worry. You can, and will, think about it a lot, that's ok, if you don't let it stop you from living your life.
And I don't know how much school time you still have, but you can find someone REALLY, I mean, REALLY fast. Like, REALLY fast. Without even thinking that much. And if you don't find in school, you'll find later. Lots of people do it, why can't you? Just don't go after someone just because school is almost over, if it's not natural, it's bad. Real bad.

That's like asking "IS IT BAD IF I MASTURBATED TO ECCHI HENTAI ON 4CHAN?"

yea you are too young, I had my 1st girlfriend when i was 18 so its too early to think about spouse, start to panic when you are close to 30

Yes, you are too young. Unless you are on board of a ship/plane that is going to crash right now. Then it's time to shout "is there a chaplain?!" tip: both aircraft/marine captain can do the job but maybe they will be quite kept busy - you know - trying not to kill everyone in their service. Grab first single female(if preferred) at least remotely close to your age and marry her.

Easy.

You are never too young to think about your future. You are too young to get worried about it though. High school relationships don't last very often. Most people at that age aren't that serious about relationships and are too young to settle down. You will meet many more people in your life. At college, work, going out, other social events even internet.
Dreaming of a nice future with a nice spouse is never wrong ofcourse. I think most people want that in the end. Being insecure at that age is quite common. But you really aren't in a hurry.

"I saw in here that there are people who are older than me"
Yes you would hope so,

Also yes to the other question,

Masturbation is the right answer!

"How can I find a girl after I've finished school?"
University, work, internet, mutual friends, etc.

Don't overthink it and try to let it happen naturally. As they say, love is like a fart. If you force it, it's probably going to be shit.

There's no "real" age limit to think or fantasize about things themselves.
Getting married in particular is one of those things that "eventually happens if it feels right", so no need to actively "worry" about it.
Just go on with your life, focus on things you like doing, pursue your interests and develop yourself as a person. :)

Google for

• Mötley Crüe - Too Young To Fall In Love

There you will find enlightment.

Sorry, you missed your chance

15-16 is when most of the 1st world countries allow marriage to occur. But in general it can be easier to wait until you are 18, as many require parental consent before then.

at 15 years? nah

Here's the crazy thing: You can think about whatever you want, whenever you like. School is only one of socializing chances; there's work, neighborhood, friends in common, hobbies, activities...

Live for today and tomorrow will come naturally.

Yep, too young.

You can always move to some shitty country with lots of sand where you can just marry a 9y old girl. Because religion.
If that ain't your cup tea, you can still try a mail-order bride.

Are you too young? Yes. Is it normal to think about this? Of course it is! Just let life take the wheel, things will happen when it happens. No need to worry about that now :)

Dont get married dude.