This week's book giveaway is in the Open Source Projects forum. We're giving away four copies of Eclipse Collections Categorically: Level up your programming game and have Donald Raab on-line! See this thread for details.
What class are you using to represent the Date? Is it this? You will have to go through its documentation and work out which methods add 15 minutes, and which methods return the milliseconds since 1st Jan 1970 as a long. Then you can compare the value with sysdate, which you can obtain from methods of the System class.
The rest is easy.
It looks like it's time for me to write you a reality check! Or maybe a tiny ad!