There are a lot it people talking about two very different things. If I read the original post correctly, the dealer wanted to do a throttle body cleaning. This is the valve that controls the about of air going into the engine. They do get coked (yes coked) over time. I find it very difficult to believe that a cleaning service would be required at only 15k miles. Dealer’s make money on the upsell. You can ask if they would show you what they are cleaning. If it is visually dirty, then yes, it needs to be done. Can you do it yourself? Yes. I’m sure there’s a YouTube video for it. I would also use caution because some manufactures use a coating on their throttle bodies to reduce the carbon build up. Some of the other people here are talking about adding a fuel additive to the fuel tank to reduce carbon build up on the inside of the engine, as in the injectors, valves and pistons. I hope this helps.
Actually, I think the OP's dealer wanted to do an Intake Clean -- including the TB, and whole intake path. Usually done w/ some top engine cleaner induced in the air intake stream downstream of the MAF sensor (to not gum it up) purportedly to clean up the intake valves; and also a throttle body clean.
My dealer offered me a TB clean at 22k miles, which I declined.
But, it did get me wondering what the proper top engine clean interval is on these GDI's, as they will never get the valves cleaned up by the fuel.
Were it not for EGR, this would not really be a discussion...but since exhaust gasses are recirculated back into the intake stream, the intake path sees some dirty air along the way.
On all my prior GM trucks, I usually got the throttle body cleaned around 60-70k and they were fine.
But, none of them were GDI.
As a result of the upsell my dealer threw at me w/ the Throttle Body clean at 22k miles, my trust in them has waned a bit...I did have a convo w/ the general manager of the dealership on this topic; he was more in line w/ the 60k interval for Throttle Body. Last time I was in, there was no TB cleaning recommendation -- not sure if that is just for me or for everyone now.
But, this intake/top engine clean still makes me wonder a bit...realistically, there are enough of these on the road since 2019 in the trucks that I would think if it were truly "required" it would be easier to find info of people having it done...