Cruising and cottaging was how I discovered for sure that I really preferred to be with men when it came to sex. I didn't really enjoy the whole experience and after every encounter I was determined never to do it again, but was eventually always driven by some need for which I had no name. I only found out much later that sex for me was infinitely more satisfying with someone I cared about.
Undoubtedly it is potentially risky, but I never came to any physical harm. Maybe I was just lucky. Occasionally I would meet someone who actually seemed nice and with more to explore than just his bits. The great majority of people were probably sad closet cases like me who didn't know how to get it any other way. Hygiene was occasionally an issue, but not often.
The worst experience I had was in the early 1970s in a public toilet in East London. I stopped in to take a leak and two good-looking men in their early twenties (a few years older than I was at the time) followed me in and took up positions at the next and next-but-one urinals. A couple of weeks earlier an older man had given me a hand job in there so I already knew the place had potential. These two men just kind of stood there with their cocks out, not peeing, but not rubbing or playing with themselves either, which seemed a bit weird. It was as though they were waiting for me to make a move. I was tempted, but something didn't feel right. Thankfully the light dawned, before I did anything stupid ... uniformly dressed in the wrong colour (for the time) jeans, short and neatly combed hair, black shiny shoes ... this was a police entrapment. Anyone old enough to have been around in those days will know that no one looked like that unless they had to. It was the shoes that really gave the game away. Details are so important.
Back to the subject at hand (as it were). You are going to follow your own path no matter what others here say, but if I had my time again I think I would have preferred to have had my first sexual experiences with people closer to my own age and with whom I could meet in more salubrious surroundings and at least initially in a social setting. I don't know that the world is actually more dangerous now than it was forty years ago, but you owe it to yourself to make sure you are safe and that if and when you find someone to love and who will love you back you can bring a healthy and happy body to the relationship. I would also endorse the suggestions about giving yourself a bit more time if you can. At fifteen you are not just a risk to yourself, but to an older partner too.
It sounds like you are pretty clued up, though, so all the best and good luck.