Simple. As 15 years ago represents a time for you when life was exciting and fun without all the worries of today. This BF was probably young, good looking and interested in you which made life worth living and all that more fun and exciting.
It was great to show him off to your GFs and making them jealous but then life didn't play fair as you grew up and moved on and the excitement and fun as a teen was long gone and truthfully there probably isn't anyone on here that doesn't think or want to go back in time to those days, but we can't so we just dream a lot and make a lot of wishes that will never come true but then like a Garth Brooks song says, " many of Gods best gifts are unanswered prayers" and thus why we cant go back.
Besides many of us would do the same ole stupid things we did then again so we must learn to be thankful for what we had and what we have now.