After some hassles, I finally upgraded from mediawiki-1.11.1 to mediawiki-1.15.0. I do not think that the new version runs faster, but for some reason, my web site is now running faster. The web hoster has probably done something to its servers.
Mediawiki is still a great tool for recording what I have learnt everyday.
I have finally completed building the web site for a company setup by a former colleague. I am using the Joomla package. This CMS is far better than the previous one I was using.