This answer record serves as the Vivado 2015.4 tool update 2 (2015.4.2) Release Notes, and contains links to information about what is included in the update.
The Vivado 2015.4 tool update 2 (2015.4.2) is a cumulative update which provides all of the content available in 2015.4 update 1 and also addresses the following issues:
Vivado 2015.4 Update 2 provides -1HV and -1H production speed file updates for all Virtex UltraScale parts except XCVU440 parts, which do not support the -1H and -1HV speed grades
For designs leveraging these devices, Xilinx recommends installing this update.
For all other devices, please continue to use the Vivado 2015.4 release.
Downloading and installing the Vivado 2015.4 update (2015.4.2)
Known Issues specific to Vivado 2015.4 update (2015.4.2)
|(Xilinx Answer 66743)||The report_synchronizer_mtbf Tcl command does not support -1H/-1HV devices|
For Vivado 2015.4 Update 1 (2015.4.1) Release Notes see (Xilinx Answer 66245)
For Vivado 2015.4 known issues see: (Xilinx Answer 63538)
For known issues related to a specific IP, please search the support site for "Known Issues" and the IP name.