Website takes about 10 seconds to load

Hi,
I was asked to improve and to make a performance check on a website made with wordpress.

The main problem of this website http://www.terapie.org/it is that it takes almost 10 seconds to load. I asked a friend from Poland to load it and he loaded it in about 3 seconds (an acceptable time lapse).

I started to check the website using P3 Plugin Profiler and everything seem ok: it says that the most heavy plugin takes almost 2 seconds and it’s accetable.

So I check for the caching plugin ( DB Cache Reloaded Fix ) and here it is the strange thing: – if I check the bottom lines added by the plugin, I find this:

<!-- Generated in 7,451 seconds. Made 24 queries to database and 0 cached queries. Memory used - 28.11MB -->
<!-- Cached by DB Cache Reloaded Fix -->

– If my friend from Poland check the bottom lines, he finds this:

<!-- Generated in 2,350 seconds. Made 6 queries to database and 15 cached queries. Memory used - 27.93MB -->

Why?
I supposed that if it would be a server-side problem the plugins that work on that server, would have given the same results but my friend results surprised me.
So why the website is so slow? Why I get these different results? How can I fix this?

Thank you so much!