Is it normal to Date a 15 year old ?

Females lie.
Adolescent and young adult females often portray themselves to be older than their actual age; while older females often portray themselves to be younger than their actual age. C'est la vie.

Intrinsically, there is nothing wrong with dating a female of only three years age differential, at your age, however...

Due to some draconian legislation that was written long ago, by some senile, decrepit old fuddy-duddy, who is now dead, but who is still destroying everyone's life;
And because of a bunch of out-of-touch with reality, do-nothing demented current leaders and legislators, it is probably illegal to do so, where you live.
So if you want to date this beautiful young female, you will need to petition the [state, if I am not mistaken] legislature to revise and update this very out-of-date legislation.
But you will probably have better luck getting milk from a peach! And this has become nearly impossible, because the peach crop was practically wiped out by adverse climatic conditions that is happening all around the world.

So what you need to do, if you want to date this beautiful young female, is get together with all your friends (the more, the better).
You, and all your friends, pledge to physically cut and remove the penis and testicles from any sick, twisted, perverted, creepy, weirdo police-criminal(s) who interferes in your personal relationships in any way. (If it's a female, then they get a mastectomy and spayed; before they breed another one).
Of course, no one will want to do the dirty deed. So the best way to this, is to take up a collection (absolute secrecy is a must), and pay someone to do this, since there is no shortage of greed in this world. But watch out, because police-criminals are theives too! If they steal from you, cut their hands off!
No-one gets paid anything, until after the deed is done, and you and your friends are reasonably assured that they did it; but they must be assured that you are trustworthy, and will be forthcoming.
The money trail must be hidden very well, since police-criminals will follow this too.

With that said, if you want to date this beautiful young female...Since you are the older partner, you will need to behave in a mature and responsible manner.
You will need to ensure that an unwanted and unneeded pregnancy does not ensue, for at least five years hence, but probably much longer than that, since there is already too many people in this world, and we don't need any more.
It is a huge responsibility, and if you are not willing to take it on, then find an older female, who might teach you a thing or two, about the ways of the world.

See, I'm not such a bad person. I'm just a gangster-of-love.
Have fun.