I have look in source of firmware and I have see that we use apache package. It maybe better replace apache by NGINX

"Nginx is a high-performance http-server with other functions as well. It is a perfect candidate to run on OpenWRT due to the performance and memory handling."

http://wiki.openwrt.org/doc/howto/http.nginx

or other small http server which is used in openwrt gargoyle distribution:

"httpd_gargoyle -    A small HTTP server for use in Gargoyle,  An open-source web interface for OpenWrt
  Created By Eric Bishop http://www.gargoyle-router.com
             This program is a modified version of mini_httpd
               The original mini_httpd was created by Jef Poscanzer
               http://www.acme.com/software/mini_httpd/"

http://www.gargoylerouter.com/gargoyle/projects/gargoyle/repository/revisions/0ed4be5168d96443662ef6aa98af6cf247ad4ccc/show/package/httpd-gargoyle