Video codec for low power displays?

I've built a digital signage app. I want to use it on Roku and FireOS TV's since basically everyone has those as platforms and they are cheap.

One of the features I want to offer is the ability to play served video from a server to a TV endpoint, and decode it and play it in browser. However, with one of the insignia TV's I am using for testing, I have tremendous stuttering. I am serving VP9 WebM's. Is there any video codec which has an extremely low decoding cost, even at the expense of file size?

EDIT: Its possible I can get a lot of performance by using h.264, since hardware acceleration for WebM might not be a thing on these TV's. Will test when I have a moment to re-render the video