It might help to know what OS and version this is for (since vmstat for Solaris and Linux man pages don't show a -I option). And going back looking at your other post, Tru64 seems to be what you ask questions about but the man page I found for it doesn't show a -I option either.

(suggest you always post the OS and version you are seeking help about)

As far as your question - it may be an issue with security (something killing off processes that are above 2 hour limit). Maybe setting it up as a cron job would work better.