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'

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