Toward the climatic end of Rogue One, on the beach of the planet Scarif, two stormtroopers have a casual chat about something called the VT-15 being “made obsolete.” Without a doubt, this very short dialogue exchange is the most obscure Star Wars easter egg in the new film because it’s actually a prequel to a conversation two different stormtroopers have on the Death Star in A New Hope.
The “VT-15” conversation in Rogue One lasts for maybe five seconds, before those stormtroopers are taken out by the Rebels, but some of their comrades-in-arms seem to have similar interests in A New Hope. While Obi-Wan Kenobi is trying to sneakily deactivate the reactor controls which keep the tractor beam functioning on the Death Star, two stormtroopers talk to each other idly. One says to the other “You seen that new VT-16?” and the other says, “Yeah, some of the other guys were telling me about it…”
According to Wookiepedia, the VT-16 might also be called a “BT-16,” which is a security droid, similar to the spider-creatures seen skittering around Jabba’s Palace in Return of the Jedi. But, since the sources Wookiepedia pulls from aren’t considered “canon” anymore, what exactly these stomtroopers are talking about could be anything. Den of Geek! theorized that maybe the Rogue One conversation could be a vague reference to T-16 Sky-hoppers; a type of airspeeder Luke references in A New Hope, too.
Either way, Rogue One’s obscure reference to stormtroopers talking about something that is in it of itself equally obscure is the ultimate in continuity precision. Because even if we’ll never know why stormtroopers are so into chatting about these things being “obsolete” or “new,” we do know their interests are fairly consistent.