ZSystems

I noticed that currently logstash-7.8.0.tar.gz is included which rather obsolete by now (current release according https://github.com/elastic/logstash/releases is 7.15.1) Using that, however, would most likely imply that the patch files be changed accordingly as well (educated guess).

So, how to proceed with this one:
a) Stick to the rather obsolete version 7.8.0?
b) Use the current version (which might require more effort with regard to patch maintenance)?

You are allowed to update the tar archive.
Use following commands for that in the replacement:
1) osc rm old_archive.tar.gz
2) osc rm key.asc
3) Download new archive and key from the logstash download page
4) osc add new_archive.tar.gz
5) osc add new_key.asc
6) update logstash.spec with new version numbers
7) osc ci
8) If builds are failing, look, whether used patches are required (test it with removing ones)