Why not? Episodes IV,V,and VI were released 3 years apart from each other (1977,1980, and 1983) as were the Prequels (1999, 2002, and 2005)
But how soon did pre-production start? It's not like someone set a date to meet at the studio and get rolling.. before a second of footage is shot it takes months and sometimes years of work.
This is why i feel a 2015 release date (especially if it's in the summer.. July 4th for example) is too soon to deliver quality product.
I'd rather they take their time and find the best screenwriter/director duo they can find before we get another Phantom Menace.
Perhaps Episode 7 has been in the plans all along, long before today's news.