I doubt there were ever plans to launch a 3DS successor in 2015. Basically it was always just a guess from certain "experts" in my opinion.
I agree, considering that they launched in 2011. 4 years long lifecycle for a console that it's not repeating DS numbers, but (to me) is still selling more than decently (ww, especially in Japan), and that is aiming at 60+ millions LTD would be very strange imho.
I can understand doubts about wii U lifetime, but not 3DS ones.