It's all very well for us 'seniors' to scoff lightly about how you haven't lived, and how you'll get your heart broken loads, and all that other stuff that comes from experience but ...
at fifteen, you are concerned with the here-and-now, not what may or may not be in the hundreds of years until you reach our ages!
So, the majority of advice is sound - you cannot live your life protecting yourself from life itself, or you never really live at all - just exist.
I guess you feel frightened and excited in equal measure right now?
Concetrate on fhe exciting part, and push the fear away, it gets in the way.
You must remember this - you won't actually die of a broken heart, although sometimes it may feel like it! So, if it's not going to kill you, it has to be worth the risk to see if the rewards are there.
You will meet plenty of guys, some nice, some rotten, and yes, some may break your heart, but that's part of learning how to love and be loved.
A famous philospher said "What does not kill us makes us strong ..." and that is certainly true where relationships are concerned.
Remember, don't fall too hard too fast, take things a day at a time, and enjoy the experiences, good and bad.
Good luck!