Hey there, @D0m3 
Welcome to Netlify Forums! 
Thanks for reaching out!
First, I want to draw your attention to our newly released Next.js Essential Build Plugin! This link also contains Docs references and an open source repo that you can access 
Second, thanks for reaching out with this question! Currently, if you use Next.image on Netlify it can be slow because we make a Netlify function for each image that you use. Currently our team is working on this. In the interim, one of our Next.js experts recommends using Cloudinary. Should you be curious about next.image on Netlify, you can also check out this repo!