The problem with 2015 is i just don't see them having a good enough lineup ready and assuming a big power jump games are going to take even longer. I do think the 3DS should have a shorter span than the DS, but then again i think the ds was pulled faster than it should have been. The next handheld also shouldn't launch above 149
The DS was pulled because it was dead in the water in Japan and fairly dead in Europe.
I mean yes it was still doing well in the US, but the concern was everywhere else.
As of this Fall, Nintendo will have released Pokemon, 2D Mario, 3D Mario, Brain Age, Animal Crossing, Mario Kart, Friend Collection, Zelda, Nintendogs, and Mario & Luigi, and third parties will have released games like Monster Hunter and Kingdom Hearts.
There will have also been a wide variety of niche interest games released in almost every genre, including attempts at new markets on Nintendo handhelds like Resident Evil: Revelations.
There's not much in the way of known sellers that are likely to come out for the 3DS that haven't already been delivered. Obviously moving the price of the system is an option, but I don't see a lot of other obvious avenues to continue to push growth or even sustain sales momentum for a game perspective.
The two that come to mind are Dragon Quest and potentially Super Smash Bros, or a mystery game that's a huge success, but if that's all that's left for the next two years, they want to be planning ahead.
If the next system is releasing in a bit over two years, they could simply start diverting a few teams for the launch window now in order to have support ready.