that looks like samsung's very old before One UI. i don't remember how to get rid of them. unfortunately all my samsung devices are running a much higher android and they are all running on One UI so i can't troubleshoot for you.
i would look into using a different launcher. i have been using Nova Launcher from day one. the only issue might be that your device is so old i'm not sure if any launcher will run on such an old android os.
has this always been like this? or did this just happen?
TouchWiz was Samsung's launcher before One UI. So it would be the default launcher on your Android 5.1 phone. (Or in other words, you didn't inadvertently 'turn it on', it's an integral part of the firmware installed on your Prime and is always running in the background.)
Instead of fixing the problem with TouchWiz, by installing Nova you're just adding a more feature-rich launcher on top of the existing one.