use defaultDate()
Set the date to highlight on first opening if the field is blank. Specify either an actual date via a Date object or as a string in the current [[UI/Datepicker#option-dateFormat|dateFormat]], or a number of days from today (e.g. +7) or a string of values and periods ('y' for years, 'm' for months, 'w' for weeks, 'd' for days, e.g. '+1m +7d'), or null for today.
try this
$("[name=trainingStartFromDate]").datepicker({ dateFormat: 'dd-mm-yy', changeYear: true,defaultDate: new Date()});
$("[name=trainingStartToDate]").datepicker({ dateFormat: 'dd-mm-yy', changeYear: true,defaultDate: +15});