Q: Apple TV lagging

Recommended settings for Wi-Fi routers and access points - Apple Support

the ATV4 has an ethernet connection, you can test further by connecting the device directly to the router. You should also disconnect any other device that may be downloading, streaming or using up bandwidth on your router.

Intermittent problems are often a result of interference. Interference can be caused by other networks in the neighbourhood or from household electrical items.

You can download and install iStumbler (NetStumbler for windows users) to help you see which channels are used by neighbouring networks so that you can avoid them, but iStumbler will not see household items.

Refer to your router manual for instructions on changing your wifi channel or adjusting your multicast rate.

There are other types of problems that can affect networks, but this is by far the most common, hence worth mentioning first. Networks that have inherent issues can be seen to work differently with different versions of the same software. You might also try moving the Apple TV away from other electrical equipment.

The following article(s) may help you.

Troubleshooting Wi-Fi networks and connections

Recommended Wi-Fi settings

Sources of Interference

Wifi Diagnostic Software (for Mac users)

You may also find some help on this page, where I’ve collected some of the more unusual solutions to network issues.

I actually missed the wired part, but yes you can still get interference in cables, but it's much less likely.