Wordpress backend too slow, even after wiping out all expired transient ans session in database

It seems like my issue has not been here before, so I have created a new thread.

We have an e-commerce website and currently the back end is pretty slow. I did delete all the expired transient and session in database (before it was 1.2 GB but now is 200 MB). But the issue is that the admin site still slow and data is growing fast.

We have a lot of plugins and I am not sure if they are involved in this problem. We are using Wordpress version 4.2.2 and WooCommerce version 2.3.8, so I am thinking about upgrading them to latest versions, to make the admin site working faster as possible.

I hope that someone can tell me how to fix this issue. We struggle with this issue for a while. Thank you in advance.

Cheers

via Chebli Mohamed