If you are having performance issues on the backend (in your dashboard) you might want to check on how many pages you currently have. WordPress was not meant for over 100 pages as it will start running into memory issues. This won’t affect the front end load times, but you will want to start banging your head against your desk. I had a client recently with a little over 1,000 pages and it brought WordPress to a crawl. And yes they are on a high-end VPS. It doesn’t have to do with the server, but rather how WordPress is structured.
Ticket related to this issue: #15459[alert-note]Update: This is no longer an issue and was updated with WordPress 4.2, Changeset 31730[/alert-note]
WordPress Mentions This Limitation In Their Documentation
Note: this parameter was planned for Pages. Be careful, when choosing it for your custom post type – if you are planning to have many entries (say – over 100), you will run into memory issue. With this parameter set to true WordPress will fetch all entries of that particular post type, together with all meta data, on each administration page load for your post type. Src: Function Reference/register post type (Update: Codex was updated in January 2016 to remove this as it is now mute)
And in layman’s terms…
Pages have a hierarchy tree. So in the WP dashboard, anything to do with a page ends up having to load the entire page hierarchy tree to distinguish how that page relates to others. When dealing with a post, you don’t care about other posts, only the date of the relative post, so you don’t have to lead nearly as much.
Remember, WordPress was originally built to be a blogging platform. Even though some people might not view it as that anymore.
Start using and taking advantage of custom post types. WP Beginner has a great introduction on how to start using custom post types in WordPress. There are even plugins available if you need to convert your pages into custom post types.