We think the style and script is not slowing your site, It may be because of your image size. So you can use online tool to reduce your image size and upload. And as you asked there is no functionality to remove just portfolio style and script. To do that you have to edit theme core files. But while editing theme core file make sure to create child theme so that when you update the theme your edits wont get overwrite while updating the theme. We hope you can understand.