bigfootz,
I use Float Tube Force Fins and they're pretty adjustable fore and aft and over the top of the boot but, if your boot is just too wide, then there's no need to further investigate. I can check the max width of the fin tomorrow, if you're interested.
[You must be registered and logged in to see this link.]Do you use your Korkers for approach and tubing/wading? If so, and your having problems finding fins, may I suggest using dedicated approach or hiking shoes and then a flats boots to tube - might open up more choices and save some needed real estate for the fins. You can just store you boots in the rear deck of your tube (or in your case, they may need their own float tube
) For short walks, they're fine. A couple hundred yards down a dirt/slightly rocky boat ramp at Heenan was no problem this past weekend. But if you're hiking say a few miles, then you'll want to pack your gear and I'd imagine you'd want make the hike as comfortable as possible. Not much ankle support in them so, YMMV.
Another thought - I use Simms neoprene guard socks with my wading boots to wet wade creeks when I fly fish, weather permitting (you'd probably want the regular neoprene socks as the guards aren't needed.) They're a little thinner than my flats boot I use specifically for tubing (and hopefully someday for hunting bonefish on the flats
) Since you probably have stocking foot waders, at a minimum, I'd slap something like them on if I needed to try to cram the 15's in a fin with minimum footwear. I'd imagine you'd want to protect the waders' stocking feet as much as possible. Direct contact and rubbing may damage the foot of the waders. With a neoprene sock, at least you'll just sacrifice it rather than the waders themselves. If you have a short walk to the launch area and you wear you waders, you may want to use some Crocs to get there. Crocs Off Roads have adjustable heel straps (something you may need.) BTW, I use waders and those Crocs for wintertime surf fishing; lightweight and won't corrode. I just worry the sand may ruin my waders foot though.
Good luck.