Configure Eclipse to pre-bundle App Engine classes into a single JAR for faster warm-up

Question

After some discussion with a colleague from another company that also uses App Engine, he told me that he managed to cut down his app warm up time from ~15 seconds to ~5 seconds

Answer 1

He argues that during instance warm up, since the instance need to load only a single bundled WAR file instead of thousands of separate classes, the warm up would be significantly faster. Any thoughts or opinions about this?

I doubt it. WAR is just a ZIP file, which gets unpacked when it's deployed on the server. So there is an additional step, meaning the process can be equally fast (if unpacked when uploaded) or slower (if unpacked when instance is spun up).