Carb counting is current, carb exchanges are not.
Yes, 15 g of carbohydrate is usually equal to 1 carb exchange… But nutritional labels on food didn’t exist when carb exchanges ruled, though when they were introduced varies by country.
I was diagnosed in 1988, 2 years before nutritional labels were required in the US. Prior to that, we had no idea how many grams of carbohydrate were in what we ate. We may have had a diet book with some generalized info, but it could be far off from what was actually in the food. We also had slower insulin, thus we learned to eat to our insulin regiment, rather than dosing for what’s on your plate. With carbohydrate exchanges, you had a set meal plan… Something like 3 carbs for breakfast, 2 carbs for am snack, 3 carbs for lunch, 1 carb for afternoon snack, 4 carbs for dinner, and 2 carbs with protein for a pm snack. You took the same amount of insulin at the same time everyday, plus you had a “sliding scale” of extra shorter-acting insulin you added for correcting highs. Then you had to learn things like 1 carbohydrate exchange = 1 slice of sandwich bread but only ½ of a bagel or English muffin, or 8 oz. of milk, or 1 small apple or orange, or 10 french fries, or ¼ cup of cereal…
This notion of exactly how many grams equals a carb exchange didn’t really enter the picture until people were trying to recognize these new nutritional fact labels with the already familiar exchange system. (Yes, there were some more fastidious endos who more thoroughly trained patients prior to that, but it was not common place.) As we obtained more specific food knowledge, we drifted more to the I:carbohydrate ratio for dosing, and away from eating a required amount of carb to satisfy the insulin you took.
Just because you happen to know that 15 grams of carbs equals 1 carb exchange, doesn’t mean you’re following an exchange system… Unless you are actively trying to eat the same amount of carb every day at the same time. If so, then yes, you’re following an outdated system.
When Humalog first hit the market, I was told to take 1 unit for every 15g of carbohydrate, despite being a small child. I think that was just a generalized rule for everyone to stick with the exchange system we already knew. To this day, I still haven’t strayed far from that original 1:15 ratio, though. I’m currently using 1:13, and from what I’ve read, the vast majority of diabetics have an I:c ratio fairly close to 1:15, so in that regard the old carb exchange system might still be relevant.
I suspect you just talk about exchanges now as an easy way to recognize a defined amount of carbohydrate I still find that information useful more then 30 years later, since I make everything from scratch and most of what I eat doesn’t have a nutritional label.