Quay doesn't control download speed since it links directly to S3 for image downloads. Quay.io is hosted in the us-east-1 region on AWS. We advise users to check the network connection to this region using a tool like speedtest for aws.
If that does not provide any insight:
1. restart docker daemon
2. provide the output of a timed docker pull $ time docker pull quay.io/<insert your repository name>
3. provide version of docker $ docker version
4. if users use AWS and it's possible, place their ec2 machines in us-east-1
5. use a VPN. This may cause more number of hops, but lower overall latency
6. verify that there are no DNS issues in the network