This post relates specifically to Telligent Community 5.6, but could be relevant for other versions.
When looking at a Telligent Community site with a large number of posts (in this case more 380,000), viewing a list of posts with popular tags can lead to the page timing out.
Adding the following index to the database can reduce query time, this reduced some queries from 70 seconds to 6, not brilliant, but much better.
CREATE NONCLUSTERED INDEX postCategoryIndex ON [dbo].[cs_Post_Categories] ([Name],[IsEnabled],[SettingsID])