What is a good way of saying "run this after 15 minutes" on a shell?

You are searching for at (at@wikipedia)?

usr@srv % at now + 15 min
at> YOUR COMMAND HERE

You can define multiple commands that should be executed in 15 min; separate them with a return.
Confirm all commands with control+d.

I use a short script I keep in my path, called after, containing

at now + "$@"

This way it's very easy to, for example, type:

after 15 min

then any commands and Ctrl-D, or

echo COMMANDS | after 15 min

which does the same.