Also, if your Chromecast is slow because lots of other people are using your wifi network, then consider buying a wifi access point (wifi AP) to connect to your router, then set up another wifi network just for the Chromecast to connect to. For best results, have the wireless AP plugged into your router with a cable and position the wireless AP as close as you can to your Chromecast, to give it the best signal.
Of course, this is only useful if your wifi bandwidth is being used up, not your internet bandwidth 😉