It is also worth mentioning that it may also be high packet-loss between you and your DSL exchange, typically these issues are amplified the further away from your exchange you are. The number of consumers using the same copper telephony network can also aggravate this.
To check whether DNS is indeed partly contributing to your sub-optimal network performance take a look at this: https://www.grc.com/DNS/BENCHMARK.HTM
- An excellent utility with knowledge of several DNS servers. Don't forget, geographic position does play a significant part when it comes to DNS latency, as the packets won't have to travel through as many hops (typically).