I was rooting around YouTubes as one does when a number of (hah) zeros caught my eye: 10,018,000. That was the view count on the PlayStation upload of the Final Fantasy VII remake announcement trailer (there's an additional million views between the Square Enix North America and Square Enix Japan pages).
That seemed rather high and indeed that video (10M) outpaces Uncharted 4 (3.6M), The Last Guardian (3.1M), and Horizon (2.4M) as far as E3 view count on the PlayStation channel goes. For context, though mostly for fun, I went to check on Nintendo and Microsoft's channels and E3 videos.
Microsoft tops out with Halo 5 multiplayer (3M; the campaign trailer is at half a million), Nintendo with its World Champions event (3M). It's worth noting that Nintendo and Microsoftt's YouTube have a third the subscribers of PlayStation's (1M to 3M).
This is to say nothing for how many people might have watched these things live, nor does it offer a barometer beyond general curiosity, people who sought out or just clicked a video (Mario games will sell like water in a desert, Nintendo YouTube view ticker be damned, because they have Mario).