There's a server version of the JRE (Java runtime):
"For deploying Java applications on servers. Includes tools for JVM monitoring and tools commonly required for server applications, but does not include browser integration (the Java plug-in), auto-update, nor an installer."
This makes a lot of sense, all that you need. Couldn't find it in AUR. Guess, that's because it's not there. Maybe that's because nobody knew, yet. That's why I'm writing this post. I've no clue how to build an AUR package and quite frankly am not really into it but I'd be pleased if somebody who's down in the trenches could create one. The archive contains only the binaries+native libs and visualvm, that's it. 15MB.
Did you have a look at the AUR PKGBUILD for the normal JRE and adapt it?