I use Digicamcontrol to tether my Nikon Z5 to a PC with Windows7. In session set up I tick for send 'JPEGs only' on the assumption that this will speed things up (when back home from the studio I process files from the SD cards, so I do not need the raw files on the studio's tethering PC.)
BUT, the raw files do get passed across as well as the JPEGs. Apart from possibly slowing things, this is annoying because I have to click though a duplicate of each pic when reviewing them. Any idea what's going on anyone?