How much time required for Software Development?

My company has recently finalized SRS document (which has been written by me) from the processes involved in software development and the documentation involved it seems like this software development will atleast take 1.5 years for completion; is it that length process?

 There is no silver bullet for development. It means that there is not standard measurement for time of a project. Timeline is defined by customer and development team can adjust it as per system description. Development time estimated also depends upon type and functionalities of a system . If development time is 1.5 years then it is quite huge project. A project can take 1.5 years or even more for completion.