I think your whole site is generally slow(not just your forum): 7.48sec to generate the page. I've had this problem with some of my Joomla! sites and for the most part i've resolved them by cutting out unnecessary scripts/images and compressing others. Check error logs to see if any particular third party copmonent/module/plugin is causing the problem - because not all these have been developed by professionals.
I find Anthony Ferrara's joomlaperformance.com website a great free resource for Joomla! users of all skill levels. There are loads of articles dealing with Joomla! performance and benchmarks etc., the article
So, you want to speed up Joomla?
is a good place to start. The website also has a
performance grader
as well as offering the free query cache component.
Other Resources I would recommend using are
Content Optimizer
(which optimises and caches images in your site) then uses either
Minify4Joomla
or
CssJsCompress
(both do the same job by optimizing and compressing CSS/JS file)
Basically cutting out necessary stuff will decrease the page load time - then you can think about optimizing/compressing scripts .css files and images or even enabling page caching. It's not a Kunena issue (at least i don't think it is) - although you can expect your forum to have a slightly slower page load time than the rest of the site when finished - but this would be minimal.
