If you've got so many songs ready (at 15!), that's amazing! Congratulations, and don't stop writing. But now, keep in mind that you need to present a whole new artist brand to the world if you want to be heard, and that brand is more than your music. So, before looking for an answer to the "how do I promote myself" question, build *what* to promote first.
It doesn't have to be too overwhelming. If you're just starting:
1. Pick one or two social media platforms you're most active on already, or want to focus on the most at first.
2. Ensure that all your online profiles (ideally including a website) look consistent: social media handles, profile image and other graphics, short bio, etc.
3. Experiment with the kinds of posts you share on your artist profiles, with the goal to come to a confident and somewhat consistent voice (don't be afraid to express your opinions).
4. Start releasing your music, song by song (e.g. 1-2 per month), don't rush into releasing too many too soon. Find someone to create quality cover artworks. Distribute all or some of the songs on digital stores and streaming platforms. See the reaction on each song, and consider releasing an EP with the tracks you believe will perform best based on what you've heard from people so far.
5. Only only then, once you've started defining your brand, and once you have a content and release strategy: work on getting more people to hear your music. You will find a number of marketing ideas and tips here on the Hub, and I will be glad to elaborate on that more when I learn more about your project.
These are just a few general recommendations. To see a more clear path, set more specific goals. You will get "there" if you try to go "somewhere", that's for sure :) But it may not be the destination you want. Know what you want.