If you want initial full backups to be processed quickly, it is recommended to use a larger worker instance profile, and then change it to a smaller profile for incremental backup. You can change worker instance profile settings on a regional basis, so make sure that the worker instance size is appropriate to process the largest workload within the required time.
Each worker instance is deployed as an amzn-linux-v2 image, and the binaries are downloaded from the connected S3 bucket. Instance types of worker instances sizes depend on the total EBS volume size.
Processing EBS volumes under 1024 GB (default)
Processing EBS volumes between 1024 GB and 16 TB (default)
Processing EBS volumes over 16 TB (default)
Processing EBS volumes under 6 TB
Processing EBS volumes over 6 TB
For details on AWS pricing, see AWS Documentation.