Most artists take about 2 years for each album as far as I know.
Linkin Park had album releases in 2000, 2003, 2007, 2010 and 2012... Also huge gaps 

Apart from the last one. only 2 years, you don't even know how happy i was to hear they'd be releasing another album already 
 
Anyway, if Demi releases one album every 1.5-2 years then that'd be enough in my opinion. Obviously I'd like more, but I'm not sure if in the long run, for the general public (and for Demi herself), that'd be a good idea 
