It's a straight swap. 128 GB for 128GB. The only thing I'm changing is the colour. Although I'm not sure if I Will go out today as I'm not feeling too well (flu). I may just try and make a reservation for tomorrow if I'm feeling better.
Hope you feel better soon and get to swap the iPhone. I had a silver 6 plus for a year, moved to rose gold 6s this year. Still undecided. Love the smaller size, but battery isn't great. Only half of my 6 plus