get a 10mm round notched floor trowel and using your angle grinder bore it out to 15 to 18 mm!! works great on large format on walls or floor greatly reducing the need to backbutter!!
a larger trowel is good carefull not to go beond the depth of the rec.thickness of adhesive,if the walls are very good go for up to a 10mm trowel if the walls are rough dont tile it.large tiles and rough walls dont mix
For this size tile on uneven walls you would have to use a 10mm trowel and back butter the tile as well or use a 15 - 20 mm trowel with cement adhesive as a full coverage of adhesive has to be made on the back of the tile