How to deal with having to use very large background images

I work for a small web agency. My designer/boss wants me to integrate this image as a background for all the pages in a new website I'm integrating: http://ift.tt/1Rh1MIa

There's a lot of content on the homepage, so she just made this image that spans over 3000 pixels of height. She's done this multiple times in the past and I've repeatedly told her it probably wasn't a good idea, and how it affects the loading time of the page. But she won't hear it and really wants me to make something extremely close, if not identical to her design.

I've been able to sometimes identify recurring patterns in her images and make a repeatable background out of it in Photoshop. But in this case, I'm not sure how I could handle it without simply yielding and actually using a 1800x3400 image as a background image for every page. The only way to optimize it I can even see at this point would be shrinking the image a little bit and stretching it across with background-size: cover

Any ideas? Are there techniques/solutions I'm missing?

Epic visual tool

Epson 5030UB 2D/3D 1080p 3LCD Projector Submitted November 30, 2015 at 05:45PM by trauma_pigeon http://ift.tt/1ToeYu3