Android 11: App polling interval is not 15 minutes minimum?

I've been reading some web forums on e-mail clients, like for K9 on
Android where users complain they were forced to 15-minute minimum mail
poll intervals.  Some users don't have IMAP servers that support PUSH,
so they rely on very short poll intervals to react on e-mails within a
very short time they remain viable (e.g., 2FA codes that expire, job
contracts sent to a list of freelancers where the first to respond gets
the job).  The users thought a new version of K9 had implemented a
change to 15 minutes between mail polls from the prior version that
allowed down to 1-minute polls.  The conclusion was that Android 11 had
a restriction that apps were not allowed to poll servers at less than 15
minute intervals.
When I check IMAP PUSH, it only works in clients on the Inbox folder.
If the server moved a new message into the Junk folder, PUSH isn't used
on that folder for the client to see a new message show up there.  I can
get 2FA codes via e-mail that end up in the Junk folder, and those codes
expire, and often far shorter than 15 minutes.  I cannot whitelist the
2FA codes, because the sender is unknown to let me add them to a
server-side rule trying to keep them out of the Junk folder.  Just
because I'm trying to log into a site that issues a 2FA code doesn't
mean that is the host name that sends the code.  Besides, user-defined
rules are exercised AFTER the server has already applied its spam
filtering, so user-defined rules are ran too late.  The false positive
has already been moved into Junk, so it isn't in the Inbox folder when
the rules get ran.  One of my e-mail accounts has a Safe Senders
whitelist which overrides the server's spam filtering, but other
accounts have no such whitelist that is effected before the server's
spam filtering.
Does Android 11 have a limit (which seems unpublished) that IMAP apps
cannot poll at shorter than 15-minute intervals?  That would suck.