I would remove the image sizes that you don’t need.
function remove_image_sizes() {
remove_image_size('image-name');
}
add_action('init', 'remove_image_sizes', 99);
Whilst the number of images is a factor, I’d also look at the image compression as this may be a big help in reducing the disk space required:
add_filter('jpeg_quality', function($arg){return 70;});
You will need to re-generate your images for this to take effect. Try the Regenerate Thumbnails plugin. Alternatively, you can run a command line like convert.
Here’s a guide: https://www.howtogeek.com/109369/how-to-quickly-resize-convert-modify-images-from-the-linux-terminal/
One final method to remove the WordPress default images is to set the dimensions to 0, as per this article;