Everyone improves at their own pace. I think that the convenience of viewing other people's work and successes online has created a very widespread and unhealthy mentality of "oh god, 8 months out the womb and I still haven't made it?? It's over for me lads..."
Because of this, people (creatives, especially) are always walking around with the idea that they need to be a smashing success and reach their desired level of skill as early as possible, but it's just not going to be that way for most people, and that's okay. It takes time and practice (in the right areas), but more importantly, it takes a different amount of time and practice for everyone.
Assuming you're 15 years old (you said earlier that you were going to turn 16), you should accept that there are people who are 15 years old, and draw better than you. There are also people who are 15 years old and draw better than me. Finally, there are also other people who are 35 years old and draw worse than you, me, or anyone ITT. I've been at it since either 2011 or 2012, but only in the past few 2-3 years have I felt like I'm making art that could be viewed as objectively decent. There are people who started drawing later than I did, got better than me, and did all of it far quicker. And it's completely okay, because we all learn at our own pace.
But, also - you're always just going to have bad days regardless of skill level. Being "good" is not going to immunize you against the occasional self-deprecative thought that you're bad and should be far better and everyone's doing better than you etc etc.
I really like this image, because it makes something clear that isn't immediately obvious: more often than not, the reason why you start viewing your own work as "garbage" is because your mind is advancing to the next level, and increasing your standards and knowledge - your skill just hasn't caught up yet, and it eventually will.
The important part is that you take your time and don't give up (and that you don't wait an agonizingly long time to start practicing fundamentals like I did). And, more importantly - you're in your teen years, there is no need to pressure yourself this hard. You're doing completely fine and have plenty of time, don't beat yourself up over your peers being slightly farther ahead.