The minified css would not make much of a difference in load time. That font awesome css file references the paths to external font files that will load in after the page loads. You can see the delay on font awesome's website: https://fortawesome.github.io/Font-Awesome/icons/
@font-face {
font-family: 'FontAwesome';
src: url('../fonts/fontawesome-webfont.eot?v=4.5.0');
src: url('../fonts/fontawesome-webfont.eot?#iefix&v=4.5.0') format('embedded-opentype'), url('../fonts/fontawesome-webfont.woff2?v=4.5.0') format('woff2'), url('../fonts/fontawesome-webfont.woff?v=4.5.0') format('woff'), url('../fonts/fontawesome-webfont.ttf?v=4.5.0') format('truetype'), url('../fonts/fontawesome-webfont.svg?v=4.5.0#fontawesomeregular') format('svg');
font-weight: normal;
font-style: normal;
}
You could base64 encode the fonts and include them right in your site's css. This would substantially increase your site's css load time, but it would get rid of the flash. Although it might not work in all browsers and I would not recommend it.
You could try hosting the font awesome css and fonts directly on your server. The CDN might be the cause of the latency.