By default Apache loads lots of modules. If you are running only Drupal based websites on your VPS / Server, you should consider disabling un-needed Apache modules. This will save lots of memory and optimize server.
How to disabled Un-needed Drupal Modules
Here is a detailed tutorial how you can disabled un-needed / un-necessary Apache modules.
How to Disable Un-neccesary Default Apache Modules
Minimum required Apache Modules for Drupal
Here is the list of minimum Apache modules which is required to run Drupal websites. I have tested this on a Drupal 7 website.
mod_alias mod_authz_host mod_deflate mod_dir mod_expires mod_headers mod_mime mod_rewrite mod_log_config mod_autoindex mod_negotiation mod_setenvif
You can safely disable all other Apache modules on your server / VPS.