LOW TIME RESPON FOR HTTP AND HTTPS WEB BROWSING

Hi there
I installed a peplink balance 710 combining 3 wan connections, but when a user opens an http or https page, it is not instantaneous, you have to refresh or once or twice or more before it opens and sometimes not at all;
on the other hand, when I connect my pc directly to one of the modems, the http or https pages open quickly
what to do to solve this?
Regards