Hi Frederic and welcome to our community!
That isn’t normal, so we’ll be happy to investigate. Could you give us the URL of the site that is slow? It would also be useful to find the single slowest request that Netlify is involved in, and send us the value of the x-nf-request-id HTTP response header as described here: [Support Guide] Netlify Support asked for the 'x-nf-request-id' header? What is it and how do I find it? so we can help troubleshoot.