https://forums.xilinx.com/t5/Welcome-Join/xpr-file-opening-older-version-of-vivado/td-p/644137
Open Windows and search for regedit.exe (Registery Editor)
Go to HKEY_CURRENT_USER and search for Vivado.Project.1 and update the default parameter with 2015.1 (you will see 2014.4 in your case)
