Our cluny 1400 is in the garage waiting for installation. We took the more conventional approach, with the four burners you chose, but subbing the 18K burner for one of the two pairs of induction hobs. We do use the 18K burner all the time on our first Cluny 1400 (liked it so much we did second!). We are not vegetarian, do like to put a hard sear on meat, but high heat is still useful for searing and browning vegetables, boiling water (though I'm interested to see if we use the induction hobs to do this as we get used to them). Surprised you cook a lot but never use a wok, but you never know when the urge to stir fry may rear up, and that can be vegetarian, pescatarian, or full on carnivore. Plus I like the look of the gas hobs, seems to fit the classic style of the LC better than flat induction plates. No interest in a plancha. Hate the cleanup. But we have friends who use their griddle all the time. Different strokes. No wrong answers.

Do you ever stir fry on your 15BTU burners presently? Is it large enough for your biggest Le Creuset? A large pot of water may be too large relative to the coil in the larger induction ring on the two burner hob. The version available in Europe has a bigger diameter for large pots.

Not so much stir fry (because the 18K is better for that), but certainly use the 15K for high heat when the 18K is already occupied. Say, browning meat for a sauce while boiling water for pasta. And our largest Le Creuset fits fine there. Compared to most standard ranges, 15K is a lot, though not so much when you compare to some of these semi-pro style ranges that push 20K ore more. But for my cooking, I like the 18, but the 15 is a good alternative.

I guess my question back to you is how often you anticipate using four induction hobs simultaneously, versus wishing you had an 18K gas burner.