Have you done a network scan to check what other wireless networks are in your area?
If there are many neighbours all trying to use the limited channels then this could be the cause, especially if they've also started streaming or gaming. Modern routers will automatically channel hop to use a free channel if one is available, but if your locality is congested, wireless can slow down dramatically.
If you can route a cable, it would be far better if you had a wired ethernet connection between your router and TV rather than wireless. Wired is both faster and interference free.
