deco router

Just need some simple advice. I currently have a TP-Link Deco X60 system setup in my house. Three Decos, all hardwired with either cat5e or cat6. The internet comes into the house through a cable modem, Arris SB6190, then into the main Deco, then into an unmanaged TP-Link 8 port gigabit switch...

Whenever anyone uses this tv in my house the internet slows down to the point where a google search takes a while to load. It effects everything connected to the internet like computers, phones, etc. The TV is a Samsung Series 7. I do use a wifi extender...

I have fiber optics, ethernet gives me 600/600 up/dn, however when switching to wireless, cant get above 170/160 This is the same as my old service that could not get above 150dn (15up) standard. I did not see an option to change the channel. The router is 15ft from my current device, so...