Greasy Fork

History is overflowing.
It's good to make updates to the url parameter "t" not every second, but after 15 seconds.

Oh I didn't notice. In that case I think it makes more sense to change the url only when pausing. There is a new version, feel free to customize it:
function listen(){
const video = findVideo()
video.addEventListener('timeupdate', () => {
const seconds = parseInt(video.currentTime)
if(seconds % 15 === 0){//divisible by 15
changeUrl(seconds)
}
})
}

Here is a version that stores time locally https://greasyfork.org/en/scripts/455475-youtube-resumer