Performance degradation in Payload after upgrading Next.js

Describe the Bug

After upgrading Next.js in our project, the overall performance of Payload has significantly degraded (e.g., response times are much slower). Downgrading Next.js restores performance.
This issue can be reproduced using the Payload multi-tenant example by upgrading Next.js to the version mentioned below or newer.

Link to the code that reproduces this issue

https://github.com/payloadcms/payload/tree/main/examples/multi-tenant

Reproduction Steps

1. Clone the multi-tenant example from the Payload repo.
2. Upgrade Next.js from 15.2.3 → 15.5.4 (or newer).
3. Start the project and log in.
4. Interact with the admin panel and API endpoints.
5. Observe that response times and overall performance are significantly slower compared to the previous Next.js version.

Which area(s) are affected? (Select all that apply)

area: core

Environment Info

- payload: 3.59.1
- next: 15.5.4