> Any suggestions to politely tell the hiring to be quite is welcomed.
> I'm pretty sure they know our company's policies as they are HRs ;)

Asking folks to be quiet in an open office space is unlikely to be effective. 

You could talk to them and ask if they could do their job elsewhere or more quietly, but realistically much of their job probably involves talking. That's going to be hard to change.

Instead, consider methods that don't involve changing others. Read: https://workplace.stackexchange.com/questions/778/are-there-any-strategies-you-can-use-to-remain-focused-when-working-in-a-open-pl

If you have't already done so, talk to your boss. Explain how this impacts your productivity and ask if there is somewhere else you could work.