Domain mapping slowing down my multisite a lot

Hi Guys,
I've started to have problems with the domain mapping plugin. It slows down the website a lot (with 20 seconds).
Last week everything was fine, but all of a sudden the website started to load very slow. I deactivated all the plugins and reactivated them one by one and I discovered that when I'm activating the domain mapping plugin the website the website goes almost unresponsive.

Could you please help? I've activated the support access.

Thanks in advance!