PHP script of WP plugin takes 11 seconds to load

I’m no .php expert, so I’m looking for a little help (or at least an explanation)

A plugin I’m using on my organization’s site (called Coin Slider 4 WordPress) is slowing the site to a crawl. I ran a full page test on pingdom tools and the plugin’s .php file (coin-slider-4-wp.css.php) takes more than 11 seconds to load. The .php file itself is only 1kb, and nothing else is particularly slow.

Here’s a screen shot: https://i.stack.imgur.com/Z1o4h.png

And here’s the text of the .php file in question:

/* Coin Slider jQuery plugin CSS styles
https://workshop.rs/projects/coin-slider
*/

.coin-slider { overflow: hidden; zoom: 1; position: relative; }
.coin-slider a{ text-decoration: none; outline: none; border: none; }

.cs-buttons { font-size: 0px; padding: 10px; float: left; }
.cs-buttons a { margin-left: 5px; height: 10px; width: 10px; float: left; border: 1px solid #B8C4CF; color: #B8C4CF; text-indent: -1000px; }
.cs-active { background-color: #B8C4CF; color: #FFFFFF; }

.cs-title { width: 920px; padding: 10px; background-color: #000000; color: #FFFFFF; }

.cs-prev, .cs-next { background-color: #000000; color: #FFFFFF; padding: 0px 10px; }

#coin-slider-coin-slider { width: 940px}