For now, the update is being rolled out to the unlocked variant (XT1540) of the handset in North America and Canada. Beside bumping the Android version to 6.0 and adding all the new Marshmallow goodies, the 2GB update does not really bring much to the table.
It does remove a few Motorola apps like Migrate and Assist, which should not really come as a surprise since Motorola had announced this change earlier this year.
Motorola had previously already updated its flagship handset for 2015, the Moto X Style/Pure, to Marshmallow, and recently updated the Moto X (2014) to the latest version of Android as well. It is also conducting soak tests for the Marshmallow update for the Moto X Play in some regions of the world. Now with the Moto G (2015) now receiving the Android 6.0 update, the company has done an astounding job in quickly rolling out Marshmallow to its devices.
Thanks for the tip Alex!