You may remember in Lollipop that Google made the option for you to reinstall your apps from another device, or set it up as a new device. Well Samsung has come out with their own version of that feature, called Samsung Smart Switch. Which mostly only works with Samsung devices, however, you can sideload the APK and it'll work on any other Lollipop device. Smart Switch allows you to transfer your data from or to the Galaxy S6 and Galaxy S6 Edge. It's not perfect, but it is a great start to the feature. The app even allows you to transfer data from iOS devices as well as Android devices.
Looking up the app on the Play Store on the web shows that it's mostly only compatible with Samsung devices. However, it does show it's compatible with the Alcatel OneTouch Idol 3. Which is a bit surprising, and appears to be the only device that it's compatible with that's not a Samsung device. But that's not really an issue, as we stated, you can simply sideload the APK, which is linked down below.
Quite a few things can be transferred using Samsung Smart Switch. For Android users, you can transfer "Contacts, calendar, text messages, photos, music (DRM free content only, Not supported for iCloud), videos (DRM free content only), call logs, memos, alarms, Wi-Fi settings, and wallpapers" to your new Galaxy S6 or Galaxy S6 Edge.
Samsung says that all Galaxy devices running Android 4.0 and up are compatible. Starting from the Galaxy S2 range and newer. That's quite a few devices actually. And it's nice to see that Samsung hasn't forgotten their users that haven't upgraded in quite a few years. Seeing as the Galaxy S2 is now approaching 4 years old.
To sideload the APK, simply download it from the link down below onto your device. Now go into settings and tap on security. Make sure "Unknown Sources" is checked. Now open the APK you downloaded it and it should go through the install process. After a few minutes, the app should be installed and ready for you to swap over your data to the Galaxy S6 or Galaxy S6 Edge.
Download: Samsung Smart Switch