The problem here is not with Perl but with CGI. Your situation is comparing CGI to Servlets/JSP and the differences between the two mean that Servlets will normally win on performance.

Mod_perl is for apache so yes, you won't get it to run on IPlanet. However, I think it is a little harsh to consider re-writing the whole app. Have you considered writing a middleware server that abstracts all your database code?

That way you can keep a large majority of your existing database code (plus abstract your database from your view) and then just re-write your view? I've used this approach with great success here but, peversely, in reverse with a Java backend and Perl frontend. Just my 2p :)