Hi:
The v7.15 is found under the windows 7 drivers section.
It's not supported to be run in W8.1, so I don't advise updating to it, unless you have a way to install W7.
You make the change of operating system near the top of the support page.
Software and drivers for
HP Pavilion HPE h9-1150t Phoenix CTO Desktop PC
Detected operating system: Windows 7 (64-bit) Choose a different OS
Here is the direct link to the W7 BIOS update file...
This package provides an update to the IPIWB-PB Motherboard BIOS for the supported desktop models and supported operating systems.
7.15 Rev. A Windows 7 (64-bit) Dec 5, 2012
https://ftp.hp.com/pub/softpaq/sp60001-60500/sp60068.exe
- Updates Intel Memory Reference Code to v1.0.017.
- Resolves issue with loading HP Vision Diagnostics.
- Resolves intermittent system hangs when 32GB memory installed.