Abe wrote:

Why not avoid any potential problems and just buy a 15 amp breaker for
a few bucks?
..
Exactly:

Had one situation where we realzed that a circuit extended out to shed
from a 20 amp circuit included some #14AWG.

We quickly changed out the 20 amp breaker to 15 amp not because of any
problems but a) to meet code b) Demonstrate for an in impending
insurance inspection (the first in the 36 years since house was built!)
that wiring was built and maintained to standard.

Reminds me got one cracked duplex at the bench must change it. And
although its indoors think I'll make the first one on that run a GFI.