How to install Windows 7 on a 2015 MacBook Pro? The SSD on my 2014 MBP cratered the other day. While it's off at the shop, my employer bought me a new one.

The problem: I need to dual-boot into Windows 7. Boot Camp Assistant in OS X El Capitan refuses to use anything older than Windows 8.

Notes:


I'm a developer. Some of the libraries we're using will not work under anything other than Windows 7. I'd love to update them - hell, I'd rather just use OS X all the time - but that isn't going to happen.
I cannot use a VM. Really.
Because 3D acceleration under any available VM - Fusion, Parallels, VirtualBox - sucks. 
Yes, I actually need 3D acceleration to do my job. 


I went ahead and flashed a USB stick with the Win7 ISO and installed rEFInd. rEFInd will not, so far, acknowledge any USB drive that I have. I've tried two different USB sticks (both USB 3), nothing.


Really, don't suggest a VM. It's not going to work for my application. At all. Seriously. 


All things considered, I'd rather just downgrade this thing to Mavericks. Life was easier and it didn't have this ugly flat gray dock, amongst other things.
I would recommend just installing Windows 7 as you would with Windows 8 +.

Substitutes:

Hold down the option key while turning on your computer instead of using refind, this will give you a boot menu.

Uncheck all the options in boot camp, except the option to install drivers to a usb stick.

Go to disk utility, make a new partition, and set it to MSDOS FAT.

Start up your Mac, booting from the usb stick(hold down option key while turning on your computer). When prompted for an install disk, choose the partition you made. Go through the rest of the install process, and then plug in your driver usb. Find the setup.exe, and go through the it's install process.

Then you should be all set.