Thank you very much Gekker!
This makes a big difference of course. Reducing both frame rate and resolution by 50% reduced the GIF to 7 MB, only 10 times rather than 40 times larger than the original. _ 🙂 And of course, quality is reduced.
I was naively expecting too much of GIF. Wikipedia says:
With the introduction of widespread support of the HTML5 <video> tag in most web browsers, some websites use a looped version of the video tag generated by JavaScript functions. This gives the appearance of a GIF, but with the size and speed advantages of compressed video. Notable examples are Gfycat and Imgur and their GIFV metaformat, which is really a video tag playing a looped MP4 or WebM compressed video.
Thanks again!