I take a protein shake after every tough ride. I use a hydrolyse protein (30g protein/serve) and then make up the carbs myself, sometimes with just rice milk (30g carbs) on bigger rides I add maltodextrin based on ride kJ, how many carbs during etc.
I like to have the flexibility of changing the amount of carbs depending on the workout, but I get the convenience of an all in one product.
I come from weightlifting background and am trying to maintain some muscle.
When I tracked my calories recently I found I tend to have lots of carbs when training hard and protein suffers, so the 30g protein shake aids in immediate recovery and boosts overall daily protein. Win win
Edit: to answer your specific question. I’d choose the ON gainer. You can get away with much more than 15g of carbs