i have the same wordpress with heavy graphic hosted on the same server.
using my 5MBps fiber, its lightning fast.

but my fleshly install Winter load damm slow (it took 4 second before the page title loaded.)
It not the 1st time visit, it happen every time.

dresscode.com.my ( my winter theme prestashop )
i4tos.com ( my wordpress )

I've just checked with our network and did not see as your report from 2 difference frameworks. It's work as normal with speed. When i click a menu About in prestashop and click Home It took 9"47 to back to home page and do the same with wordpress and it took 11"02. I think it work fine. You can try with other network to test it

Best Regards

Also, when develope we disable the cache and other perfomance settings. After done your site, you can turn on cache and performance to make it load fast as possible.

Thanks!