Piped. It uses SponsorBlock to also skip ads by the creator in the video, I am very sure they will update it to remove ads injected by YouTube as well. It is also very privacy-friendly.

That sounds very much like the idea of SponsorBlock (but might need a bit of refinement to work for different ads of different length). You should definitely check out Piped for watching YouTube videos without any tracking/ads/dark patterns, I am very sure they will do something to remove server-side ads as well (hopefully).

And if it is just five seconds instead of 15, it would be way better!