A 2015 MBPro will have the traditional reliable scissor mechanism. Apple abandoned the dreaded butterfly keyboards with the 2020 models (maybe even the late 2019 model, but I'm not certain on that).
Be careful purchasing a used Mac from a unknown source or vendor. Many vendors don't properly prepare a Mac for sale and people end up discovering a previous owner can still control the used Mac, or the Mac may have a firmware lock enabled on it.
If you purchase a used Mac, I highly recommend you perform a clean install of macOS by first erasing the whole physical SSD and re-installing macOS. I also recommend creating a bootable macOS USB installer as well just in case Internet Recovery Mode (Command + Option + R) doesn't work out so you have more options available. This will also alert you to whether the Mac has a firmware lock enabled, and hopefully will alert you if the Mac is still being managed by a previous owner (no guarantees on the latter). If either of these two conditions exist, there is nothing you can do to remove either one so return the Mac for a full refund if this happens. People should always perform a clean install on any pre-owned device just to make sure there are no nasty surprises left over from a previous owner.