Bought brand new in 2017, upgraded the RAM to 32GB since. No longer have the mouse.
The machine works impeccably and has no blemishes or marks or any sort of damage.
Have the full package, including the brown exterior box in which the glossy carton goes in.
It has the flash drive so it's blazing fast. Been using an external (USB 3.0 ~500MB/s load speeds) SSD drive to install huge games and other apps (including bootcamp Windows), so storage wise there's no limitation here.
Full Specs:
Late 2015, 5K 27"
i5 quad core 3.2GHz
32GB Ram
250GB flash drive
Radeon R9 M390 2GB
Currently with Mac OS Mojave, upgradable to whichever version you want.