If it's your own page, you might try putting the Vive camera video in background. Doing passthrough AR, I regularly used Vive (and now WMR) down around 30 fps. But I displayed the browser directly in the HMD. So no WebVR display latency. And I don't do lens correction (old laptop with integrated graphics), which has a bit of a "comfort mode" effect. And no predictive tracking, so the rendered graphics have lag, but no judder. And displayed directly, it was easy.[1] So YMMV.
Depending on your level of desperation, there's my largely-abandoned WebVR-like stack for Vive on linux. But I didn't get around to supporting A-Frame, just Three.js. But by keeping it simple, some things the complex native WebVR stacks have struggled with these last 2 years on Windows, were much easier.
[1] https://cdn.rawgit.com/mncharity/node-webvr-alt-stack/master...