nethunter can be installed over any android OS underneath, and you will have 90% functionality, as for an S6 if there is not a prebuilt image and kernel already available;

https://forums.kali.org/showthread.p...r-kernels-repo

its doubtful anyone would create one now for such an old phone.

Check out nethunter docs for how to install it on any android phone, no root required;

https://www.kali.org/docs/nethunter/