If you disable DNS, you'll really see slow - like no connection at all.
Either use the one your WiFi gives you, use the router address itself (the Gateway address) or use Cloudflare (1.1.1.1 and 1.0.0.1). (Cloudflare is faster than even Google.) For mobile data, either the one your carrier gives you or Cloudflare (if you can change the DNS setting).
But understand - DNS just gives your device the numerical address for the canaonical address (in other words, you put in "aol.com" and it gives you 124.108.115.87. That's all DNS does. Changing the DNS server you're using doesn't change the speed of your connection.)