Beside the swapping question which got answered a lot (indeed very expensive and unrealistic unless you got lucky stumbling on a cheap one someone is trying to get rid), I will comment on the movement...
I have the Grey 15500 since one month and upon receiving, it's 5 mins too fast and something is wrong with it so I sent to oascom to service it. He said it's overoiled with cheap oil and dirty, hence why it's not running right but after servicing, it's running +1.4s/d now. The decoration is put with double-side tape on the movement and the rotor wasn't installed properly so it's rubbing.
Miyota 9015 is a nice reliable movement but please service it when you receive the 15500 so it will be working reliably.
If the 9015 is broken, I think a new 9015 can be put without modifications since what you see in the caseback is decorations hiding the true movement.
Hi, is the rotor of the 15500 loud or it is a quiter one?