I'm with you on wanting TouchWiz removed from S5s, and a lot of other people are as well. Someone else asked about this earlier, so I've cut and pasted my answers below:
"You can’t really turn it off, unfortunately. You can root the device and flash a new ROM, if you want to go down that path, but of course that will void your warranty.
Probably the most effective thing you can do without root access is use a different launcher to replace the TouchWiz launcher. I’d probably go with Nova, available on the Play store. Also, go into settings and apps and disable as many of the TouchWiz functions as possible, except of course the ones that you do like. You can also sideload the Google Now laucher and change the wallpaper to standard Android wallpaper for a different appearance."