Would this work? I think I can get it working under Debian Stretch, but not sure it would be a very efficient use of the machine.
Most of my not for work, home PC use is done under AntiX, so it seems silly to run Debian to run virtualbox, to then run Antix, Win/7 and experiment with other linux distros. Note that this would be on my Dell Inspiron 15-7559 which has been tricky to get things running on due to the mixed nVidia and Intel video and 3840×2160 graphics, as well as the weird secure boot stuff.
I have a win7 VB install that I run under antiX. No problem. Running in VB effectively usually depends on hardware support for virtualization. Sometimes systems are capable but the features are disabled by default, so check your bios if necessary.