I would set the wireless router to the 5 gigaHertz mode. you can also have the 2.5 Ghz one on as well. with the wireless setting there should be a maximum bandwith setting. 300MB per second for 2.5GHz and 400MB/sec for the 5GHz one with the channel selection on both to auto.
If you still have issues then:
If you have something like a netgear router ( other routers also support QoS (Quality of Service) settings. with netgear click the advanced tab under setup. you can enable WMM (Wi-Fi multimedia) settings. There are also some other settings like enabling Internet QoS. There might be a setting for QOS priority list. If you set the router to assign you devices to a static address. Read the router manual to do this most consumer routers make doing this easy under the advanced settings.
Then you can put your devices like the appleTV and your laptop as the top on the QoS priority list.
Your router will give priority to multimedia traffic (like games or other network hogs, like video). If the router support a QoS list then doing the extra steps to assign IP addresses and adding them to the priority list insures that those devices come first.
I hope this helps
Though I don't have first-hand experience, I understand that the app Beamer for the Mac does an excellent job streaming to Apple TV and Chromecast. It does cost $20 and requires Mac OS X version 10.10 (AKA "Yosemite"). You can try it out before you buy.
Get Beamer here: Beamer – Stream video files from your Mac to Apple TV and Chromecast
A review:
Beamer 2 review: Drag and drop to stream any video to an Apple TV