15 trillion bid requests isn't the best metric to use. The SSP I used to work for had 150ish DSPs attached, of course not all of them received bid requests for

15 trillion bid requests isn't the best metric to use. The SSP I used to work for had 150ish DSPs attached, of course not all of them received bid requests for a given incoming impression, no point sending a banner bid req to someone only interested in video. But yeah, bid requests are more of a function of auction participants rather than unique impressions. And we all know how ad infested websites can be these days, if you have say 10 ad spaces on a page, and 100 DSPs want to bid, you're looking at up to 1000 bid requests generated from a single page view. (OpenRTB has support for sending multiple impressions in a request, but when I was there, very few of our DSPs had implemented it).