pg_upgrade 13.6 to 15.1?

Hi,

I'm fairly new to postgres; but have databases with about 2TB of data.  

Trying to upgrade from 13.6 to 15.1, pg_upgrade complains with:
[postgres@pf ~]$ /usr/bin/pg_upgrade -b /usr/local/pgsql/bin -B /usr/bin \
  -d /mnt/db/var/lib/pgsql/data -D /mnt/work/var/lib/pgsql/data \
  -s /tmp -U postgres
Performing Consistency Checks
-----------------------------
Checking cluster versions                                   
This utility can only upgrade to PostgreSQL version 15.   <=====<<< ??
Failure, exiting
[postgres@pf ~]$ /usr/bin/pg_upgrade -V
pg_upgrade (PostgreSQL) 15.1
[postgres@pf ~]$ /usr/local/pgsql/bin/pg_upgrade -V
pg_upgrade (PostgreSQL) 13.6

This is on Mageia Linux (mga9/cauldron) where the package manager prevents
the installation of both PG13 and PG15; so I have PG15 officially
installed and PG13 manually installed in /usr/local.

Due to the database size, I have the working copy on a 4TB NVMe SSD
mounted at /mnt/work/var/lib/{pgadmin,pgsql} and an identical copy on an
18TB platter at /mnt/db/var/lib/{pgadmin,pgsql}.  Both copies are
currently at 13.6.  

Rather than mess with the config locations; I use symlinks to point to
the database which are currently:
/var/lib/pgadmin -> /mnt/work/var/lib/pgadmin/
/var/lib/pgsql -> /mnt/work/var/lib/pgsql/

Nothing I read implies the need to upgrade to 14.x first...  Right?

Thanks
Pierre