Samsung just rolled out the October security patch for the Galaxy A3. It is distributed as firmware version XXU2BPJ1 to all units in Europe. This update beside the Android security patch for October, it brings Android 6.0.1 Marshmallow. Now this should make it silky smooth.
As the update just started rolling out, it may take some time for the update notification to pop up on your screen. If you are that impatient, try to check for updates manually by heading to your handset’s Settings menu.