Hi there lonesight, let me be the first to welcome you to the forum.

And man, only 15? That's plenty old enough to be a mad pixeller. Think practice, not age.

Just a little bit concerned about this one:

It looks like you used a smudge tool or something like that. I'm not sure if you did, but thats how it appears. If so, I have to point out thats not regarded as pixel art, or is using any kind of "pixel-generating" tools. That is, anything that removes you from working on a pixel-by-pixel basis. So, just straightening that out

Well, theres alot I could provide advice on, the best ways you can improve your work is to use less saturated palettes, and to work on your shading (which currently is predominately what is referred to as "pillow shading").

So you might want to check out some of these tutorials on shading

That's the base of what I have to say, it looks like you're enjoying yourself, so keep it up.