Following on from the suggestion made by Kimber on https://moodle.org/mod/forum/discuss.php?d=213138 I have created an optimised version of Collapsed Topics for Moodle 2.3.2 (2.2 version proving tricky because of Internet Explorer and tables).
It can be downloaded from https://moodle.org/plugins/pluginversion.php?id=1519.
Client side script loading time should be reduced by around 0.4 / 0.5 of a second acccording to testing on my environment. And hence your user's course page load time.
Note: That due to core API changes you will need Moodle 2.3.2+, version 2012062502.05 (Build: 20121005) or above to use it. If you get a 'pink' box when upgrading then this is an indication that you need to update your Moodle too, so you should be able to leave CT as is and perform the upgrade in one step as per standard Moodle upgrade procedure.