Samsung is rollng out Android 6.0.1 Marshmallow on its Galaxy A5 (2015) in select markets. At the Launch Galaxy A5 2015 comes with Android 4.4 KitKat and received the update for Android Lollipop around May 2015.
The update comes with firmware no. A510FXXU2BPF9. It includes all the goodies of Android marshmallow like Android’s Doze mode, Google Now on Tap, granular app permissions, and more. Along with these the update is also packed with enhanced TouchWiz UI features and the Google’s latest security updates.
Although samsung has just starts rolling out the update in Europe and South Africa. But still it may take some time to reach you if the OTA notification hasn’t popped up on your Galaxy A5 (2015). However you may check it manually also for the update by going through the Settings of the phone.