I just saw this .. holy crap, 40 views and no one knows the answer ? 🥺 But it could be for the same reason I’m stumped which is “ Siri radio “ ? ( I have no clue what that is ..linked to an Apple device..? )
However, if you’re simply referring to the GT’s standard NIT / radio, and assuming the 2015 has the same radio as in the 2013 cars ( which is what I have ) if I recall correctly, I think this is how to reset your preset stations :
Use the buttons on the left side of the radio to select the band you want ; FM 1, FM2, AM, etc.. Then use the buttons on the right hand side to find the frequency / station you want : the arrows will automatically scroll and stop at the stations with sufficient signal , or you can turn the round button which will manually get you to the station frequency number you want to set in memory . When you get to each radio station you want , press and hold the numbers buttons in the center panel for about 3-5 seconds and it’ll set that station in memory, overriding anything which was preset there before I think you can only do that with buttons 1 - 6 so just 6 different stations presets possible , but that’s for each band you chose .
It’s been at least four years since I’ve done this so not 100% certain of what I posted, but I think that’s how it’s done .
Hopefully by tomorrow someone who knows how to operate the NIT system better than me, will chime in here with the right instructions, if mine are not correct ..

 

I'm so sorry for not clarifying Siri is what they call the satellite in the car I will try tomorrow what you described with the satellite radio I am not really that impressed with the radio but I have to keep in mind it's from 2015 so it's not state-of-the-art . Thank you again for the info

 

Ah... as in short for “ Sirius XM “ satellite ? I’m guessing that’s selected via the “ Source “ button on the left which you use to switch between basic radio, or , iPod ( if you have that plugged in ) or , satellite radio .. but whether basic radio or satellite , the right hand buttons and the press and hold numbers should work the same ..