I’ve never been able to bring myself to ascend a 3-rune game either. By the time I get to zot, I know I can win — why not go for the bonus round? I don’t think I’ve won (though I cloned my save file one time to try both 3 and 15 one time and did technically win the 3). My closest was a wipe on sentinel island at 13-14 runes.
Huh, this seems like a new way of thinking about Crawl to me as I've only ever won three and four runes, and I've never collected more than six in a single game. So it still feels like a huge gap from that to 15!