Samsung Galaxy S6 makes use of tweaked touch wiz interface and folks at XDA have ported Galaxy S6 theme for the Galaxy Note 3, Galaxy S5 and Galaxy S6. The only requirement is that you need to be on Android 5.0 lollipop in order to install these. You can check it by going to settings > about.
Download Samsung S6 theme for Galaxy Note 3, S5 and S6
1. First of all enable theme support, if you don’t have it, by doing this —> http://forum.xda-developers.com/show…&postcount=146
2. Flash this V2 of theme (I adjust Calendar icon) via recovery or unpack manually if you don’t have recovery (uninstall previous version before)
3. Apply Theme from Theme Chooser of Touchwiz
4. Now choose if download Note 4 Launcher S6 Style (smaller icons and menu 5×5) or S5 Launcher S6 Style (bigger icons and menu 4×5)
5. Unpack the one you choose and put in system/priv-app/TouchwizHome (or TouchwizHome_K depends on which device you’re) with correct permissions (rw-r-r)
6. Reboot and Enjoy.