Why is my app slow in production?

I recently deployed my new Next.js 14 app to Vercel and noticed it takes quite a while to even show the page... navigating to other pages is slow as well.
However when I run
npm run build
and then npm run start on my machine everything works nice and fast as it should. Did I maybe do something wrong while deploying? Any help would be much appreciated.

Live site: https://bt-snapgram.vercel.app
Source code: https://github.com/boristenkes/snapgram
GitHub
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GitHub - boristenkes/snapgram: Under construction...
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