IMG is extremely expensive. That's true for the Summer League, camps, and the full time program.
Kids generally love it. It's beautiful. The beach is nearby. They play a sport. Mom and Dad aren't around. They hang out with other kids. They won't be overly supervised. Kids like all that.
That doesn't mean your son becomes a better baseball player.
He will be plenty good enough to play either in the 15U program or the high school program. I don't need to know anything about his abilities to say that because the League will be filled with mostly mid to lower tier players.
Why? Because most kids are playing for their Summer teams somewhere else around the country and many will be trying to play the best competition possible. And they're working on getting bigger, faster and stronger, and they're getting baseball instruction...all much closer to their homes and at much lower cost than going to IMG. And maybe they're working to make some $$$, or helping around the house, or taking a Summer course, etc.
The punch line for the IMG Summer League is it's like Summer camp. If you would normally send your kid from NJ to Florida for 5-8 weeks of Summer camp and spend thousands of $$$ doing it, then this can work. Your son will have a lot of fun. Maybe he'll pick up a thing or two, maybe he won't.