if you take the 30 million units sold over 4 years of sales, you get a current total rate of 7,500,000 units per year
at the current rate, the sales of 15 million, would theoretically take another 2 years
however, it is safe to assume that since the initial release, the console sales per month/ per year, have decreased at a steady rate.
taking the decrease per year into consideration, reaching the goal of another 15 million, could take 3 or more years.
here is a time line of the nintendo home console releases
1983/1985 - NES
1991 - SNES
1996 - N64
2001 - GC
2006 - Wii
using past trends as a measure future releases, a Wii 2 is due next year.
this is interesting
historically the nes was very popular selling 61.91 million units. thats huge numbers for an early generation console. then the snes is just behind with 49.10 million units.
the n64 and gamecube, not so much, but together sold 54.67 million units
the wii is now popular with 75.90 million units, but nintendo is not making as much money off the wii as they did with the NES or SNES. the nes originally sold for $250 in the 80's!!!!! thats the equivalent to almost $500 today. then add the loss due to piracy of games and the numbers are even shorter.
the DS [all models] has the second highest sales of all gaming devices. only behind the PS2 by a few million. 135.58 million to 146.9 million
nintendo has learned their lesson with the N64 and gamecube. they will not release another home console anytime soon. they are right to develop the DS further.
to support this look at the gameboy, plus the gameboy advance sales of over 200 million units.
nintendo has six of the top ten best selling game consoles. three of which are handhelds. the total number of the handhelds sold 335.78 million, the total number of consoles sold 186.91 million. thats 64% of sales going to handhelds!!!! the price of a DS is not much lower than a wii. but the manufacturing cost is most likely much lower.