El Capitan WiFi Connection Drops Continuously
This fixed it for me:


System Preferences – Energy Saver – Battery Power :
Uncheck “wake for network access”
System Preferences – Network – Advance – TCP/IP :
Configure IPv6 – Switch to “Link-Local only”


Found that above fix in the comments of this article http://osxdaily.com/2015/10/16/fix-wi-fi-problems-mac-os-x-el-capitan/