Sorry for the delay,

About the TAG module everything is clear to me!

Currently the page is managed from our client and they don't remember
exactly which filters are using.
I am sending you the results that give Joomla debug gives when you follow this steps:
Login -> Components -> K2 -> Items

prntscr.com/cl3eox
prntscr.com/cl3glq
prntscr.com/cl3fuw

Its so embarrassing for us to know that the cause of sending our site down is the
backend of k2. Hope your can give us some useful tips to fix this.

Here is the K2 configuration parameters in the database
drive.google.com/file/d/0B_7CphkekgxgeHFWWDZhMGh3dHM/view?usp=sharing

If you want some extra information regarding the site please feel free to ask.

Hello,

You can try caching that specific query.
You can also move the administrator to a separate server so you can free up resources.

I will forward your suggestion to the hosting support.
Can we modify k2 back end to not be so stressful to the database?!

Thank you!

Hacking it will render it almost un-updatable.
I would track down the slow queries and cache them, they are most likely the queries that are used when the administrator filters are being used.

You can also select the "Disable ordering compacting" setting in K2's advanced settings if you haven't done so.

Hello again!
Finally i found the source of this issue, it was a multi category plugin for k2 causing this.
That's why over the web you could not find this weird query.

I am posting here the faulty plugin Inceptive Multiple Categories for K2
prntscr.com/d4a6ao

You need to let the plugin's developer know about this so they can provide a fix.