TTFB is up to 8 seconds for a simple nextjs application

### Before opening, please confirm:

- [X] I have checked to see if my question is addressed in the [FAQ](https://github.com/aws-amplify/amplify-hosting/blob/master/FAQ.md).
- [x] I have [searched for duplicate or closed issues](https://github.com/aws-amplify/amplify-hosting/issues?q=is%3Aissue+).
- [X] I have removed any sensitive information from my code snippets and submission.

### Amplify Hosting feature

Performance mode, SSR

### Is your feature request related to a problem? Please describe:

TTFB takes up to 8 seconds for a rather small NextJS app. There's no clear way of reducing the time to get it

### Describe how you'd like this feature to work

Provide the docs or official ways to make it right. You could also use some deeper facts like "it uses lambdas under the hood" so developers could figure out what's the easiest way of fixing it.

You could also include a paid option to keep the amplify 'warm'

Start with the reported TTFB for the small NextJS app using Amplify Hosting Performance mode and SSR, including the attached screenshot. Review the official Amplify Hosting guidance and determine what documented mitigations apply, whether Lambda behavior explains the delay, and whether a paid warm option is feasible; done means publishing clear reduction steps or documenting the limitation.

Written by the indexing model from the issue text.