It sounds like your son is like a lot of very good 15 year old baseball players: very good but not the world beater type that everybody knows are immediate D1/draft guys out of high school. This the exact place my son was all through high school.
Here is the reality: there's no way to know the "chance" of one of the elite academic D1 baseball schools wanting him. When my son was in high school our goal was the same as yours: that he go to the best combination of high level academics and baseball as possible.
We did not know if that meant a good baseball D3 like Trinity, an Ivy, or a Stanford/Duke/Vandy. We kept an open mind to all of those and let the game come to him.
At the age your son is, it is very natural to wonder if he is a D1 level player. The fact is, you probably won't know until they recruit and offer him. And guess what? Even then, you won't know until he gets between the chalk lines.
But do realize that for the elite academic/baseball schools, they increasingly are able to fill out their roster with nothing but the blue chippers. The MLB draft obviously can result in them moving down their chart to more of the kids like your and my son, but that happens late.
So in all likelihood unless your son gets all toolsy all of a sudden, you're just not gunna know until they tell you.