Now this will require more thought around the order of events but for now, follow this logic:
In episode 3, Dale Cooper meets Naido in the 'mauve zone' as it's been described. There, he sees a socket on the wall, with the number 15. Naido warns him by making cutting gestures at her throat.
Naido leads him to the outside of the room, and on a roof, pulls a lever and is eventually zapped off. Dale Cooper returns to the room, and the socket now says 3.
This is where it gets a little meta. Socket 3 = episode 3, where Dale Cooper replaced Dougie Jones at the socket.
Socket 15 = episode 15, where Dale Cooper sticks a fork in the socket at Dougie Jone's home.
It's possible that Naido was directing Dale away from socket 15 as she knew its relation to a future event, perhaps Dale's return to the 'mauve zone'.
Also note, Naido getting 'zapped' from the roof, whilst socket 15 is in the room below (before changing to socket 3) and may have something to do with a) her own return to Twin Peaks, and b) Dale Coopers conscious return and subsequent waking in his hospital bed.
I'm sure it's possible to now question the order of some of the other events across the series (just one out of episode example, the sound heard on the gramophone in episode 1 links to the sound as Laura Palmer disappears whilst being led through the woods by Cooper in episode 17).
Discuss?
(edit: after doing a search at Reddit, looks like someone figured as much 20 days ago - and I know others have too, but I'm sure this is part of the puzzle to answering the finale?)
David Lynch does love his out of order story telling. I personally am satisfied that the 3 and 15 refer to the majority of each of those episodes. Twin Peaks (2017) seems more like a mosaic than the preceding three sets of stories, with more fragments making a more detailed final product.
Despite the extreme care and craftsmanship I still think the Dougie stuff went on far too long. I know Lynch loved it, but he made his point. The plugs, Fireman theater and so on could have balanced out Dougie. But then there's that clip where Lynch is being told he has three days to shoot in for one of the parts where he would have preferred to take probably a lot longer and put in the stream of consciousness and TM-obtained imagery and connections.
The 3 and 15 plugs were focused on long enough for them to be genuinely significant.
Fire walk with