Wow! 30mins is long time! How many JSP pages are there?
If you pre-compile at deploy time, then that process is essentially sequential. If you trigger compilations at request time, then each request should be in its own thread, so there maybe multiple compilations at the same time. Still, the fact that it takes 8 mins to load the first page means that there are lots of pages that are included in the first page, and again compiling those pages is a sequential process. I don't see how these compilation times can be easily reduced.
For V3 using jdk6, java compilations are done memory, in the same JVM and thread, so the fork switch is ignored.
Note that if you do a undeploy/redeploy of the WAR for every change, then you are forced to do a complete compilation of all the JSP pages. If however you make the changes directly to the deployed JSP pages, then only the pages that have actually been changes will be recompiled. This should greatly reduce the turn around time.
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