Trailer hitch + internal hub, the latter precluding quick releases or even wing nuts, is a nasty combo for removing a wheel for a flat fix. It would really help if I had a 15mm socket wrench I could stash in my saddle bag. It'd have to have a driver that would stick out along the axis of the axles to get around the trailer hitch. Something like this but for 15mm would probably do the trick if it were small enough. A small ratcheting driver might be a solution too. Any suggestions / links? Thanks!

I took an old combo 15mm wrench and cut off the open end to reduce weight, rounded off the edge with a bench grinder.
I used to carry it by placing the box end on the axle nut and using an old peice inner tube to lash it to the chain stay. I always had
a wrench and a nice rubber covered handle. I have since lost it and replaced 6 inch adjustable.

A 15mm 3/8" sq drive socket, a 3/8"M to 1/4"F reducer adapter and a 1/4" sq drive flex handle should give you a relatively light combination tool with enough "stand off" to clear the various obstructions. Add a short 1/4" sq drive extension if needed. The tool could be lighter still if you can find a 1/4" sq drive 15 mm socket but I don't think sockets that large are available in 1/4" drive.

All of these parts can be bought super cheap at any flea market that has vendors selling "Made in China" tools and they will be plenty durable for the use you intend.

Something like this would work. You could shorten the length a bit to save weight.

https://www.amazon.com/Metric-Flex-Co.../dp/B0013V7YA4

There are sheet metal sockets , hex formed in end of a tube.

used like in chainsaw field repair kits
[not sure if spark plugs are 15mm though]
Leverage is a steel rod thru a pair of holes in the tube..

I have a double end wrench in my bag a 15 / 14 combination.

marked 'made in W Germany' so rather a while ago ..

GearWrench makes a stubby ratcheting 15mm combo wrench, and one slightly longer that flexes up 180 degrees on the box end. I throw the non flex version in my tiny saddle bag and it works great.

https://www.gearwrench.com/catalog/wr...y_combination/
https://www.gearwrench.com/catalog/wr...x_combination/

15mm deep is available in 1/4 drive. does a gearwrench fit?

Wright Tool offers a ratchet, 3430, which is the size of a 1/4 inch drive ratchet, less than 5 inches overall, but is 3/8 inch drive. 3/8 inch drive sockets are readily available in 15mm. I have one of those ratchets; it is my favorite.

This is the traditional "peanut butter wrench," modern implementations are available:

The 5/8ths will fit a 15mm. https://www.google.com/products/catal...ed=0CCAQ8wIwAQ#

no

Actually 5/8" is very close to 16 mm. It would be a sloppy, and damaging fit on a 15 mm bolt.

15.875 mm to be exact. I did it on some auto nuts when I didn't have the proper socket. I doubt that there would be damage unless the OP is constantly removing and replacing the nut.

I carry this Craftsman stuby 15mm 12pt wrench

https://www.sears.com/shc/s/p_10153_1...1&blockType=G1

Search Sears for 'Stubby 15mm', they have few other models.