Instances launched from EBS snapshot (or EBS-backed AMI) are lazily loaded from S3, which probably explains slow performance, if you are doing lots of I/O operations (in my experience Windows is more I/O heavy, especially on boot).
From Amazon documentation[1]:
However, storage blocks on volumes that were restored from snapshots must be initialized (pulled down from Amazon S3 and written to the volume) before you can access the block. This preliminary action takes time and can cause a significant increase in the latency of an I/O operation the first time each block is accessed.
From Amazon documentation[1]:
However, storage blocks on volumes that were restored from snapshots must be initialized (pulled down from Amazon S3 and written to the volume) before you can access the block. This preliminary action takes time and can cause a significant increase in the latency of an I/O operation the first time each block is accessed.
[1]: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-init...