I can't be of specific use to you K-Ray as I'm a new user myself, but the only time I've found DW slow is after I've deleted all the media content and cache, which DW then takes time to rebuild for each page as I visit it. Not really a problem as it only happens once.
To answer your first question, yes, DW is working entirely with text files. There is no database involved unless a plugin you have installed requires one. This is definitely a strength of DW.
How 'standard' is your DW install? (What plugins have you added; are there and code modifications you've made)
For the topics you have converted, have you switched on 'Enable HTML' or 'Enable PHP' in the Admin settings, and if so are the topics doing anything time intensive?
Do you have 'nice URLs' enabled and have you created a .htaccess file to handle them?
As you're running an intranet, you could/should disable the DNS lookup feature in Admin->Configuration Manager->Network Settings.
If you are capable of editing the source code (
make a copy of doku.php first so you can recover if you have a problem), then you could place some timing info into
doku.php...
Place this in the line directly after
// xdebug_start_profiling(); (should be line 15) ...
$mtime = microtime();
$mtime = explode(" ",$mtime);
$mtime = $mtime[1] + $mtime[0];
$starttime = $mtime;
Then place this at the end of the file, directly after
// xdebug_dump_function_profile(1); ...
$mtime = microtime();
$mtime = explode(" ",$mtime);
$mtime = $mtime[1] + $mtime[0];
$endtime = $mtime;
$totaltime = ($endtime - $starttime);
echo "<div style='text-align:center;'>This page was created in ".$totaltime." seconds</div>";
That will tell you how long each page is taking DokuWiki to create. On a PHP server, mine typically shows:
This page was created in 0.0536398887634 seconds