No offense, but starting to code professionally with only 15 years sounds... a bit strange? I mean, I started coding with 10 (~20 years ago), and the easily available tooling was much worse back then than it was 5 years ago, but if I was your CEO I wouldn't put anyone with that little expertise and (I suppose?) no formal training on such a project alone (it's something else if you're working with a senior dev from whom you can learn). And when I was your age, I wouldn't have done anything that might put me in jail if done wrong.

Also, please pass this message from me to your CEO: He's an idiot for not letting you use version control.

Leave asap.