I am receiving timeouts with this repo, and only this repo
at URL http://download.opensuse.org/update/leap/15.0/oss/
as of 5:49PM EST.
I just updated (to test this problem), and everything was fine.
However – when you access a repo at download.opensuse.org, you are actually redirected to a mirror. So it’s possible that you are being redirected to a mirror that is having problems.
The easiest solution is to wait a few hours and see if the problem goes away (as it usually does). The alternative is to change your repo definition to use a specific mirror.
If I were having that problem, I would just wait and try later.