In my experience, it's the query time. Maybe it <i>should</i> be faster, but practically, with all the tech debt that goes into these things, it's not. I've actually experimented with different sizes for a social media app (meaning it queries total reacts, shares, etc) and 15 was close to optimal.<p>Latency is not an issue, and neither is displaying complex information. You can pull and display 400 dummy items no problem.<p>Loading time for the first "page" is extra valuable - you'd want that in 200 ms or so ideally. So one trick is load 3 items, then 30 or so.<p>Also you have to look at actual cost. Perhaps loading an extra 15 queries on the home screen costs $0.0004, but when you have 1m daily active home page uses, that's an extra $400 per day. In unoptimized pieces of code, the cost could well be 20x higher.<p>If you have a very high average user value like Jira, that's fine. But for say, a free manga site or something like imdb, you want to shave off costs wherever possible.