v11.5- v15.3 upgrade (linux)

Hi:
I'm a PG user in a big corp with an IT dept that administers a PG
server/instance that I use. It's an old install, v11.5, and we need to
upgrade to v15.3. They want to bring the upgraded DB up on a new linux vm
which has OS upgrades of its own. So it's a move AND an upgrade. There are
2 concerns....

First has to do with a jump from 11.5 - 15.3 ? Is it safe to do this given
so many major intermediate versions being skipped ?

Second has to do with the 11.5 having the perlplu extension installed. The
DBA created a v15.3 instance on the new server and tried to restore an 11.5
backup onto/into the 15.3 (as an experiment) but got several error messages
like this... "ERROR: extension "plperlu" is not available". I really
didn't need any of the perlplu procs/funcs I created, so I dropped them all
but the error persists. I suggested to drop the perlplu extension in the
11.5 (drop extension perlplu cascade) but there is a concern that it might
break something. So the question is... Will dropping the perlplu extension
break anything (given that there are no perlplu procs/funcs). Just to be
safe, "select l.lanname,count(*) from pg_proc p, pg_language l WHERE
p.prolang = l.oid group by 1;" shows that there are no perlplu procs/fns.

Finally, what is the best approach to making the server move AND PG
upgrade...
1) backup the 11.5 and restore into a 15.3 PG instance on the upgraded
server ?
2) upgrade the 11.3 DB to 15.3, back that up and then restore on the
upgraded server ?
3) upgrade the 11.3 DB to 15.3, then set the 15.3 destination server as a
replicated DB (let it populate) then designate the destination server as
the primary then cut the old server loose ? (this approach would probably
minimize DB downtime by a lot I would think)

Any other suggestions ?

Thanks for any advise/help !