A few months ago I convinced a client of mine to let me rebuild his website. His site was only a few years old, but did not respond well to any type of "corrective treatment". His site was on page 4 for his best terms and they were stagnant. After changing his site to a "faster" template and optimizing everything, his site has responded by rebounding to page 1 for his best keyword phrases to the #3 spot! Miracle? Maybe...but maybe something simpler!
Over the past few years, Google has hinted (is that even the right word?) that Page Speed will be a very important metric in determining the rank-worthiness of a website. Page speed is one of the factors which Google uses to help it rank websites in the Search Engine Rankings (SERPs).
Google determined that the faster a page or website loaded when a visitor came to the site, the better the experience tended to be. There are certainly other factors, but the one factor that leads to more bounces (a person coming to one page and then leaving) was directly related to page speed.
When a page loads very slowly, the user has a tendency to become very impatient and click away from the site. If the website is ranked high in the SERPs, then this may give cause to the user to not trust Google as much. So, Google began the campaign to eliminate slower sites, or at least punish them with lower rankings.
The main causes of slow sites? Well, Malware is a big one, but it's not the most-common. Large, non-optimized images are a huge cause of slow sites. When you have large images (file size, not dimensions) the site loads very slowly. This is frustrating to the user and they will not hesitate to leave.
To give your site a speed check, go to this site: https://developers.google.com/speed/pagespeed/insights/
It will give you all of the information you need for testing your website speed. Who knows, this may be the one thing that is keeping you from ranking as high as you would like.