My WordPress Site is running really slow

Hi, I has like to weeks by now.

My client says that site takes a lot to load, but any of my friends and in my work or my house isn’t running slow, it takes like 3 / 5 seconds maximum to load any section.

This is the URL of the website: http://asociaciontributaria.com/atrird/

The homepage may take a while because of the large images of the slideshow, but other sections aren’t working fine according to him.

Could you guys help me out and tell me if it’s the site’s fault or some problem with my client’s PC or Internet service?