I can only tell you what I noticed about the Chosera vs. Naniwa Professional, and only for those where I have owned both in the series. I have a NP3k but never used a Chosera 3k. With the 400, 800 and 2k I noticed the NP to be even denser and even less tending to dishing. Because of the smaller thickness and the absence of a base even drying — essential with magnesium based stones — is much easier. Being slightly denser makes them a bit more tending to glazing if used dry — a convenient trick for touching up. These observations were identical for all three, which I found remarkable as those stones have so different characters. That's why I dared sharing them.
As for these new 15mm ones: don't know them yet, but could be very interesting for stones finer than 800. A good chance I will have to replace one day my 20mm 400, no chance I will wear out the 3k.
By the way: avoid the 5k. It totally lacks the tactile and auditory feedback one would expect. Softer than usual with the series, and very expensive. Note the 3k delivers a final result of some 4k according to Japanese standards JIS, which is plenty refinement for a double-bevelled in Western cuisine. If you were looking higher: not so much for polishing as for further refinement of the edge with some fine bite: the Naniwa Junpaku 8k and the Shapton Pro 12k deliver quite a similar result. Don't get fooled by the figures. The Shapton is a much easier stone than the Junpaku — with its tendency to cracking, and the need of very careful handling around drying.
