The most efficient setup for your configuration would be to git clone the repo via SSH directly into the virtual machine (in a location that's accessible to the SAMBA user), mount the "remote" folder from the VM as a network drive in Windows and use PHPStorm to open the project directly from that drive.
The point is this: edit the project directly from the mapped location, do not use PHPStorm's deployment options to deploy your changes to the mapped drive. It will still be slow, but it should be a bit faster than your current setup.
To address some of the comments first, yes all the hypervisors worth building a VM environment upon have the ability to limit resource consumption and also guarantee minimums. You can leverage these settings to establish performance service levels. Establish the minimum requirements and translate that into a VM sizing. For example, a 2 core vCpu and 4GB RAM, and allocate a VM that cannot be given anymore and validate the app performance is within the requirements.
This guide from vmWare explains from that products perspective:
https://www.vmware.com/files/pdf/partners/tap/directions-vmware-ready-testing-application-software.pdf
A key point in that guide is to do your performance testing while also monitoring the hypervisor to make sure the CPU < 70% and memory is not starved so that virtual swapping is happening.
A general rule of thumb is when either of those things happen (CPU of the hypervisor > 70% or physical memory exhausted on the hypervisor) you can expect to see a degradation of performance of the VMs.
You can do the same for the storage and net IO dimensions, but this is going to be driven by the investment made in the underlying architecture. My organization puts VMs on SAN with multiple 10GB uplinks to the SAN, and that results in the VMs seeing higher storage IO than they would see with local disk.
Ideally, the organization your app will be deployed has a managed VM infrastructure with monitoring of the hypervisors being done and being proactive to manage such that the hypervisors aren't pushed to the point that creates VM slow down. If you can, get metrics on the hypervisor to understand its general performance trends, and then also track that while testing and state your app's requirements based on the assumption that the hypervisor will be managed to stay within those same parameters.
If you can't get metrics about the hypervisors resource and performance, then really all you can do is measure resource used by your OS and make that the requirement that needs to be guaranteed by the hypervisor.
Since your concern is mainly around storage IO, this blog focuses on measuring IOPs:
https://blog.synology.com/?p=146
Best Answer
IANAL If you need legal advice, by all means seek it, this is not legal advice.
If you install a copy of XP licence into a VirtualBox on a machine that it would otherwise be legal to install that licence on, and the licence is not in use on another machine, and you are not using the virtual hard drive on more than one machine, I think you're ok.
For example you probably shouldn't use XP Home or XP Embedded Editions in a VirtualBox, but your copy of XP Professional on the shelf should be fine.
My reasoning is that it is legal to use software like Parallels to run Windows OSes on Mac hardware, I don't see a big difference here.
Again, this is strictly opinion.