Back end crawls while front end ok

For quite some time, we’ve noticed the back end is much slower than the front end.

Meaning, working on and administrator side of the site is slow, it crawls, sometimes doesn’t even complete pages and we need to refresh while on the front end, the site is just fine, nice and quick for the end users.

We’ve tried using different browsers which doesn’t seem to make any difference so wondering what could be causing this?