CSS Parallax Lagging

My client requires that I have a lot of images with the parallax effect on the site, i'm using the effect only with CSS, and the whole site is lagging a lot, the frame rate drops drastically, any advice?

This is the CSS tad I use:

 .pozadina {
background-repeat: no-repeat;
background-size: cover;
background-position: center;
background-attachment: fixed; }