Wi-Fi drops since 10.10.3
Another thing to check is make sure IPV6 is configured as Link Local Only. To check go to System Preferences > Network > Wi-Fi > Advanced > TCP/IP. Also check for the Ethernet connection also. Also check the configuration of any Apple Routers and Apple Express units you may have for IPV6 configurations and change them to Link Local. I did this and my wifi is back to normal.