Vercel ISR pages are slow to load the first time

Describe the bug

When my app is deployed on Vercel I expect ISR pages to be pre-rendered so that they load quickly the first time a user hit them. But it is not the case, and it's not clear how to pre-rendered them at build time.

Reproduction

https://sveltekit-isr-prerender-issue.vercel.app

Source : https://github.com/mquandalle/sveltekit-isr-prerender-issue

Logs

No response

System Info

System:
    OS: Linux 6.2 Pop!_OS 22.04 LTS
    CPU: (8) x64 Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz
    Memory: 1.09 GB / 15.38 GB
    Container: Yes
    Shell: 5.8.1 - /usr/bin/zsh
  Binaries:
    Node: 18.6.0 - ~/.nvm/versions/node/v18.6.0/bin/node
    Yarn: 1.22.19 - ~/.nvm/versions/node/v18.6.0/bin/yarn
    npm: 8.13.2 - ~/.nvm/versions/node/v18.6.0/bin/npm
  Browsers:
    Brave Browser: 101.1.38.111
    Chrome: 112.0.5615.49
    Chromium: 112.0.5615.49
    Firefox: 111.0.1
  npmPackages:
    @sveltejs/adapter-auto: ^2.0.0 => 2.0.0 
    @sveltejs/kit: ^1.5.0 => 1.15.5 
    svelte: ^3.54.0 => 3.58.0 
    vite: ^4.2.0 => 4.2.1

Severity

annoyance

Additional Information

No response

Start with the linked reproduction at sveltekit-isr-prerender-issue and compare its Vercel deployment behavior with the reported first request. Read the SvelteKit and Vite versions listed in the report, then verify that the intended result is for ISR pages to be pre-rendered during the build so their first load is fast.