I understand the director's explanation for R2's awakening, but prior to reading that my theory was that the saber was left in Maz Kanata's possession purposefully, and that R2 sensed the saber's presence when Rey finally appeared at the resistance base.
R2 saying, "I found it" just as Rey appeared at the base, and the flashback of Luke placing his hand on R2 could relate to R2's forced low power mode and sudden awakening once a few conditions are met - Luke's desire to be found only when someone is called by the saber, accepts it, and that person meeting up with Leia (who would presumably keep R2 with her).
This question isn't about the validity of this theory, rather: is the saber ever near R2 prior to Rey's appearance on base in the movie, or is it far away from R2 until Rey appears on base?