Page loading times is one of the most important factors in any website, the quicker your pages can load the better your website will become. Page loading speeds will improve your SEO, this is one of the factors that search engines use rank your pages. Speed is also an important factor with the increasing amount of users accessing your website on mobile devices, with a faster website more people will see your content.
Here is a good tool you can use to compress any PNG for your website TinyPNG.
TinyPNG uses smart lossy compression techniques to reduce the file size of your PNG files. By selectively decreasing the number of colours in the image, fewer bytes are required to store the data. The effect is nearly invisible but it makes a very large difference in file size!