Ah i see, I would be happy to see some examples later on .-)
Even if you have a really small image, i’m not sure that you’ll win a lot going with with png or jpg. Unless you want to go with low res, but with sankey Chart, it would be a shame.
Do you have illustration in those svg? (png, jpg, anything that’s not vector?)
I would try to use a svg optimization tool (https://github.com/jakearchibald/svgomg) first, and see how it goes.
Then, because we never know, and image format may help, i would try https://www.npmjs.com/package/svg-png-converter would work in the browser.
The last solution is to look at pdf optimisation, but i’m pretty sure it’s gonna be useless here.
Tell me how it goes!