louisiana09,
Personally I don't think 15 is too young for your son to start attending a local or regional showcase or two.
Some of the posts you read about age may have really meant "it's not necessary for them to be seen when they are that young; save your money". College coaches are not going to start recruiting a 15-yr-old sophomore unless he is exceptional - they are busy looking at juniors and seniors. But if a showcase is affordable for you, your son can benefit at this age, by getting comfortable with how showcases work, and knowing what to expect when he is a little older and it does count.
Also, with you living in a small town, he can start to see how he measures up to some players from perhaps "baseball hotbeds" in your region. My son attended his first regional showcase at age 16 and it was an eye opener. He was in the lower rung of players at that showcase (one in his group was an 18-yr-old senior drafted in the 2nd round a couple of months later), but he enjoyed the experience and didn't feel embarassed or intimidated, came home very excited to work on improving.
My advice: If your son is interested and you can afford it, send him to 1 or 2 showcases that the HS coach recommends.
Good luck, and let us know how it goes!
Julie