Crippling TTFB/Wait times on Ajax call in WordPress

Hi all,

We are experiencing significant TTFB/Wait times on an ajax call that is effectively our entire site/proposition (it loads job listings on our job board). We are using a combination of WP Job Manager and Jobify – a well known and widely used combination. The most frustrating thing is that there are other sites using the same setup and they are lightning fast, so it’s not the setup that’s the issue.

Here is what I’m talking about:

A couple of things that may be important:
– the domain used to be londontechy.co.uk and we moved it ourselves to boolerang.co.uk.
– we initially used GoDaddy managed WordPress hosting – and moved to shared hosting.

We have tried:

– Disabling all plugins
– Changing the theme
– Optimising the database
– Switched hosts twice and now on VPS
– Asking our hosts to “optimise” the server.

We’re really at the point where we just don’t know what to do anymore. We love this project, but constantly have users complaining about the speed/response times – and it kills us to think of all those that don’t comment, but just leave and never return!

We’re really (really) quite desperate now, so any assistance/advice will be appreciated enormously.

Thanks!