Despite waiting time is a bit long, but Samsung did release the Marshmallow update for its Galaxy A5 (1st-gen) after the Lollipop update since last year end. At the moment, the update is rolling our in South Africa, Europe and some parts of Asia (One Cambodian user has proven the update is done on his A5). The version is 6.0.1.
This is a good news for A5 users. Normally, such major update is rarely happened on low and mid-range phone. We haven't heard any news about this update for A3 or A7 yet. We will keep you update, if any.
If you are the A5 owners and not yet received the OTA notification, you might have to go to check the update manually in Setting menu or wait while the updating reaching your device.