So it turns out that using a 16mm spanner on a 15mm nut for a year yields a nut that I can’t seem to undo with any of the tools in my collection.
Any advice on getting it undone? I’ve bought a new nut and a 15mm spanner, haha
NOTE: I am aware that I’m an idiot for not forseeing this/buying a 15mm earlier
buy a new bike
+1.
use a bench vice. crank it onto the nut as hard as possible then use the wheel as a giant lever. could be awkward…
yeah, that was my last resort - just don’t really want to do it that way on account of the wheel still being in my frame… I was kind of hoping for a macgyver approach involving a mars bar wrapper, a cigarette packet and some string. Or any of the other items on my desk…
vise grips will get it off
Take to it with a file and create two parallel flat spots. Then use an adjustable spanner.
take the fork out the frame if you want to reduce “awkward levels”…
It’s the rear wheel 
Thanks for the tip San Esteban - I don’t have a vice grip so I’ll get to it with the file tonight.
Stillson,s. They don’t rely on your hand keeping the jaws tight you just lean on them and the jaws tighten themselves.
UPDATE: Got it off after an hour of filing. Cheers dudes… I’ve learned my lesson.
buy multigrips. most valuable tool for removing old/broken/seized bits on cars & bikes.