Fix incorrect version introduced in manual pages

Several manual pages for releng/14.3 incorrectly claim that features
were first introduced in FreeBSD 15.0.

I discovered these by running:

git checkout origin/releng/14.3
git grep -F '.Fx 15.0'

Approved by: re (cperciva)
MFC After: 3 days
Reviewed by: imp, ziaee
Pull Request: https://github.com/freebsd/freebsd-src/pull/1685

(cherry picked from commit 5b9660caff69c70c9b6d9df5e04a3f21f8cf7996)
(cherry picked from commit ef4014882ee1413eba75a78f6e307e16123c63d1)