That implies some sort of wifi interference , usually between the speakers and your router, not the speed of your internet service. 

I would double check the FAQ I linked, and look for potential reasons why your speakers could be temporarily disconnecting from the router.

It also slightly possible you’re experiencing duplicate IP address collisions, which would also cause temporary disconnects, even if your speakers are wired, as the speaker ‘fights’ for the IP address with something else on your router. There’s a quick and dirty way to deal with this, although it isn’t a permanent fix. Simply unplug all your Sonos devices from power, and while they are unplugged, reboot your router. Once the router comes back up, plug back in the Sonos devices. 

A more permanent way of preventing duplicate IP address issues with your router is to reserve IP addresses for all network devices in your router’s DHCP table, something you could learn more about in your router’s manual, but the above process works short term...until your router gets confused again and Sonos does a firmware update, which involves a soft reboot of the Sonos.