the list I gave you, non had a size 15??
Humm that surprises me, they tend to make boots to fit anyone
any how, here is another great boot company, and have these in a size 15 for you, 600 grams of insulation
Stay warm and secure in the Granite 600g Men's Boots. Featuring 600g of insulation, a dual-density midsole, and Vibram™ Tsavo™ outsole, these handcrafted boots are designed for extreme terrain in sub-freezing temperatures.
schnees.com
and if they don't interest you, these folks i KNOW ill Built you a boot to your desire, not cheap, but will be of super quality and formed to fit your feet perfectly! but they don't do very heavy insulated boots
Custom Boot Systems CHANGING THE WAY YOUR FEET FEEL ABOUT BOOTS Custom Boot Systems Purchase 3D Mapping Kit Sizing Instructions Testimonials ANTICIPATION You've waited years for this opportunity. Countless phone calls and research. Practice makes perfect, breath, squeeze the shot. Your...
lathropandsons.com
a another boot for sure in a size 15 are the sorel's long item running boot, but not going to offer a lot of ankle support , but a lot less $$ too, and with a removable liner, can dry faster , or in more ways, , but I am a big fan of boot dryers, they dry without hardening leather and add yrs of service life to boots when you use them over placing boots near a heat source in other ways!
SOREL’s premium men’s boots are durably designed with comfort, warmth, and versatility in mind.
www.sorel.com
and if you really want the BOA system, they can be had in tons of boots
here is a link to a bunch that CLAIM they have size 15's in them for you, its a popular system in the ski, snowboard world!
but they may NOT be fun to walk in due to design for ski boards!
https://www.the-house.com/boa-snowboard-boots?routes={%22fs%22:[{%22f%22:%22Size%22,%22vs%22:[%2215%22]}]}