Working on further speed improvements, I noticed that Mantis sends an individual query out for every project when building the project list at the top of every page. By retrieving and caching all available projects first, the list can be built much quicker.

Added this function to project_api.php:

function project_cache_rows( $t_project_ids ) {
global $g_cache_project;

   $t_project_table = config_get( 'mantis_project_table' );

   $query = "SELECT * FROM $t_project_table WHERE id IN (" . implode(',', $t_project_ids) . ")";
   $result = db_query( $query );

   while ($row = db_fetch_array( $result ))
           $g_cache_project[$row['id']] = $row;
   }

}

Then simply call this function from print_project_option_list, line 364:

project_cache_rows($t_project_ids);