hi khalil, the max timeout we allow for builds is indeed 15 minutes! You may benefit from optimizing your site a bit (if you tell us more about what SSG or build process you are using, or what kind of site you have, here are some tips!)
We can manually extend your build time out, but we do need you to add a credit card we can automatically bill in case you go over in build minutes. If that is OK with you, add the card and let us know by replying here, we will check you have a card on file and can then extend the build time 