There's a few things at play. Functions will still stay warm inbetween invocations and will keep local any data already in the worker. We also maintain a couple different levels of cache so as to not hit ECR often.

I know we've got a few blog posts coming out over the next couple weeks on this new feature, and each tells a few bits and pieces about the story.

Depending on volume you'll probably find that Lambda will be cheaper for that workload, especially with the new 1ms billing.

- Chris - Serverless@AWS