Here's a comparison of what Square Enix managed to release within 7 years of the start of last gen with that of this gen. You'll notice they still released a lot of big-budget games after 7 years had passed in both gens. Japanese release dates are provided in brackets:
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Sixth-generation: Dreamcast/PlayStation 2/GameCube/Xbox
[ Sixth-gen started in Japan when Dreamcast was released on November 27, 1998 ]
Square Enix internally developed games released within 7 years of the start of the generation:
- Final Fantasy X (July 19, 2001)
- Kingdom Hearts (March 28, 2002)
- Final Fantasy XI (May 16, 2002)
- Unlimited SaGa (December 19, 2002)
- Final Fantasy X-2 (March 13, 2003)
- Final Fantasy XI: Rise of the Zilart (April 17, 2003)
- Final Fantasy Crystal Chronicles (August 8, 2003)
- Front Mission 4 (December 18, 2003)
- Final Fantasy XI: Chains of Promathia (September 16, 2004)
- Romancing SaGa: Minstrel Song (April 21, 2005)
- Front Mission: Online (May 12, 2005)
- Musashi: Samurai Legend (July 7, 2005)
- Code Age: Commanders (October 13, 2005)
Internally developed games released after 7 years of the start of the generation:
- Kingdom Hearts II (December 22, 2005)
- Front Mission 5 (December 29, 2005)
- Dirge of Cerberus: FFVII (January 26, 2006)
- Final Fantasy XII (March 16, 2006)
- FFXI: Treasures of Aht Urhgan (April 20, 2006)
- Dawn of Mana (December 21, 2006)
- Kingdom Hearts Re:Chain of Memories (March 29, 2007)
- FFXI: Wings of the Goddess (November 22, 2007)
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Seventh-generation: Xbox 360/PlayStation 3/Wii
[ Seventh-gen started in Japan when Xbox 360 was released on December 10, 2005 ]
Square Enix internally developed games released within 7 years of the start of the generation:
- Final Fantasy XI: Xbox 360 Edition (April 20, 2006)
- Final Fantasy XI: Wings of the Goddess (November 22, 2007)
- The Last Remnant (November 20, 2008)
- Final Fantasy Crystal Chronicles: The Crystal Bearers (November 12, 2009)
- Final Fantasy XIII (December 17, 2009)
- Final Fantasy XIV (September 22, 2010)
- Final Fantasy XIII-2 (December 15, 2011)
- Dragon Quest X (August 2, 2012)
- FFXIV: A Realm Reborn (2012)
Internally developed games that will release after 7 years of the start of the generation:
- FFXI: Seekers of Adoulin (2013)
- Final Fantasy XIII-3 (TBA)
- FF Versus XIII (TBA)
- Final Fantasy X HD (TBA)
- Untitled Action RPG (TBA)
- Kingdom Hearts III (TBA)
- Final Fantasy XV (TBA)
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As you can see, from the above comparison, it's completely reasonable and realistic to believe that FFXV will release on current gen hardware.
