NAV 2015 Posted Sales Invoice Loading Delay

Recently we have upgraded NAV from 2009 to 2015. After upgrade posted sales invoice page is takes too much time to load the data. All the posted document pages are slow after upgrade, In this posted sales invoice is very slow, it takes nearly 15-20 seconds to bring the data on the screen. Posted tables have entries from the year 2000. so we have manually archived the data till 2010, we dint find any improvement.

Could you please help us to locate the exact issue.