I'm not entirely sure I buy into the whole 'biggest cultural impact' metric for 2015 bestsellers—it's always a bit subjective and often conflates sales with real influence. Like, 'The Girl on the Train' sold a ton and definitely kicked the whole domestic thriller wave into high gear, but its cultural footprint now feels more like a trend template than something that fundamentally changed how we talk. 'Go Set a Watchman' was a massive publishing event, but the conversation was so messy and focused on Atticus's legacy that the book itself got lost. The real impact, I think, came from quieter books that shaped conversations for years. 'Between the World and Me' wasn't just a bestseller; it framed a national dialogue on race in a way that's still referenced constantly. You see its phrasing and ideas echoed everywhere, from classrooms to Twitter threads. That's a different kind of impact than just dominating the beach-read tables.
On the lighter side, 'The Martian' really bridged a gap. The book was huge, but the movie adaptation the same year made it a proper crossover event, bringing hard sci-fi and problem-solving nerd-joy to a mainstream audience. It made 'science the hero' cool again in pop culture. Meanwhile, something like 'All the Light We Cannot See' felt like it had more lasting power in book clubs and literary circles, winning the Pulitzer and keeping historical fiction set during WWII firmly in the spotlight. In the end, the books we still talk about years later, for their ideas or their storytelling DNA, are the ones that truly landed.