When you attempt to run an SI5 Report that has been imported into SI 2015, you get the following error:
The custom report or any of its sub report uses 'PhaseItems' as report data source pattern which is deprecated. To learn more how can solve this problem click Yes.
There is a Report Setting for this. Open Report Settings from the Control Panel or from the Reports tab in the Project Explorer or Project Editor interfaces and change the "Populate phase items" setting to "TRUE":
This setting can result in some lag time when running these reports.
The dtr:PhaseItems XML node that was used in SI5 added redundancy to custom Reports and caused a slower run time. This node is considered "legacy" at this point.