You would indeed 15 VPNs running in parallel, which will create 15
virtual network adapters, or perhaps one VPN product but with
15 different user accounts.
The problem of connecting processes to these
virtual adapters will become a real pain.
There will also be a big problem with each VPN trying
to set itself up as the internet gateway for the entire computer,
creating a real mess.
I think that a workable solution will be to create
15 virtual machines, where each will connect to a different VPN,
and run the processes inside these VPNs.
You could create one VM and duplicate it with only changing
the network name of the VM and the MAC address of its (virtual)
You would need a good computer to run 15 virtual machines with Windows,
and will also have a problem with activating 15 copies of Windows.
Perhaps having it work for only the trial period of Windows is enough.
If you could run the processes in a Linux VM, this will solve the license
problem, and also there exist very small Linux distributions that
take up much less resources than Windows.