PerfTips is one of the new debugging feature introduced in Visual Studio 2015. This feature help the developer to look into the performance aspects at the time of debugging the code itself. This feature will help in fixing proactively the performance issues at an earlier stage; even without performing a complete performance test.
PerfTips will show the elapsed time taken from the last break point to the current break point, or the time taken to execute the method. This can be configured to display the CPU time taken by the code snippet. These tips will be shown as a small tool tip at the right side of the statement where you have the current break point.