Mike - I think what you're saying is that the effort you expend on any given run, or in any given race, is equivalent to those running far faster.
I'm willing to say that's about 95% true.
One of the benefits of training at a high level for a long time is that runners at that level can go deeper into the well, so I think most 15 min guys can probably give more effort than you on their hardest days, but we're not talking about a huge difference.
The real difference in effort is probably lifestyle. The average (and, of course, they are outliers who hit 15 mins with little effort and to whom this doesn't apply)15 min guy expends a lot of effort planning their training, executing that training (often involving very high-mileage weeks) planning and executing recovery and nutrition, weight control, etc. There is also a lot of talent in the mix (an overwhelming proportion (like 99.99%) of the population could never get close to a 15min 5-k), but even with talent, this is far more effort than most people are willing to put in, and outside of college, the only reason to do so would be because you love to do it.
So, no knock on you for finding the right balance, and clearly you put some serious effort into your running, but I think the average 15 min guy is not only more talented, but also working harder and longer on their running than you are.
But, who cares? Just run at the level and with the dedication that makes sense for you and your life. Even the 15 min. guys pale in comparison to the elite. Unless you are making a living at this, it's all relative.