I'd not waste my money on 15-19m LEI based on what I see on my kite locations. They are pigs on LW - LE heavy with does not allow them properly turn when much more balanced and more powerful foil kites can still haul my 110kg ass on water.
On this video I demonstrate how 15m foil outperforms all LEIs on beach that day with around 80kg riders and much will to ride when they saw me riding. They cannot even get kite to turn to zenith due to heavy LE. I loaned Spleene monster door TT from friend as my normal ultimate Flydoor XL TT was at home so I was maintaining ground. With Flydoor my experience is if I can plane without kiteloop to accelerate I can go upwind. If I see that I cannot go upwind anymore I can still ride downwind to beach. I've outrun also 19m Core's and Airush Zeroes. Nitros, Turbines no match like in video. Dynos and Zephyrs - yeah right 'water carpet' what I've seen. Sorry but that the way just is.
Here is some Flydoor-tt enjoyment on water like tacking with backroll hand plants or jumping and touching down upwind from jump take-off etc.. So doors are suitable for some fun in 8kn range. Sure for 8kn prediction I probably wouldn't drive 260km to beach I am using in summer - but if you drove there and wind does not show up to promised level, it is a real session saver.
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If 12kn wind is common for you - or like storm to my location - I'd go for foilkite but as recreational rider never above 15m in size even for my weight. But it depends a lot on your location and riding style. Usually on 12kn I can start to get going 10m Speed4 lotus kite. But with 15m it is already jumping fun. Foilkite and normal-TT 138x42 - if you normal TT is very rockerish it will take power away from any kite due to drag. But with 12kn you'd go nicely on mediocre TT for LW.
Perhaps today if I were buying a foil kite of 15m size I'd check/demo Soul from Flysurfer. But my quiver today contains Sonic2 15m so no need. You can start also practising foilboarding with that kite on safer lower winds and when you get XP to foil on foil - then you can move any direction. Blasting water on same foilkite or ploughing with small LEI kite.
If Ozone dealer is closer to you (or your heart) perhaps Chrono v3 would be worthwhile to test. North Ace 15m, well it pulls but not refined touch like established foil kite brands have. Spleene X19 - stay away.. Pansh, HQ, Peter Lynn.. No what I've seen and tested myself...
But these are just opinions and probably not suited for you. But for me it allows me to practise kiteboarding.