See for yourself how fast your website loads. Go to GTmetrix.com, enter your domain name, and in about 30 seconds you'll know if you need to speed up your site.
Did you also know that Google is exploring ways to shame slow sites by labeling them with a screen "badge" that notifies users of a poor-quality web experience?
Google is still experimenting with how these badges might appear, but the graphic below is a possible example...
So what is the bottom line?
If your website is loading slow on your mobile phone, you will be labeled with a screen "badge" that notifies users of a poor-quality web experience, and your users will most likely "swipe off" and go to your competitor.