Well – let’s start with this which is something I wrote up before:
It is not realistic to make a direct comparison between the forum loading time and other pages within a WordPress site. WordPress posts and pages are static. The do not change from moment to moment, they can generally be shown to anyone (even if needing to be logged in to the site) and the data underpinning the display is very lightweight.
Forums are completely the opposite. On a busy forum, the data can be changing and being added to second my second – often with many users adding content simultaneously. This makes for a very rich environment but the cost will always be the extra ‘work’ the code and database has to do to load up a view. Remember too that the forum display is uniquely tailored for the current user loading the page. One user will see a different view than the next user depending on what the have and have not read, what their forum permissions are and what forum or topic they may be looking at. And even on a quiet forum, the checks and changes are still required.
I would suggest taking a look in our codex at this page however: https://simple-press.com/documentation/codex/installation/installation-information/performance-notes/
But – having said all that – I was out when your post arrived and I looked at it on my mobile phone on the local 3G network. I loaded your forum in fact and was really rather surprised that you should call this slow. Back now and I have just loaded it on my laptop and again – I see no great slowness. In fact, I would say quite the opposite. It looks to be humming along very nicely. If you are seeing a serious slowdown then it could be that something is getting loaded and slowing things down because you are a WordPress (and forum) admin.
As to the ads – no – SP has no effect whatsoever. But the speed of ads to display is dependent upon the server they are being loaded from. All requests to third party servers is going to slow things down a bit.
By the way – your forum does not look good on a phone. This is because you are not using one of our more recent and responsive themes. Not sure about your Wp theme – I did not go outside of the forum page.