As you have found out only the newly created persistent disk will have the increased size. At this time if you want to increase persistent disk that have already been deployed you will have to do it through vSphere and then increase in Windows.
I have written about how you can do this for exsisting virtual machines along with changing the pool for new virtual machines that are deployed. This can be found by following the link below:
I hope this helps.
I have the same problem and tried accessing the suggested link but page doens't load. could you please suggest where is the information.
We've found it's best to update the pool and recreate the VMs with new persistent disks.
These days everyone should be moving away from persistent disks to solutions like Liquidware ProfileUnity and VMware User Environment Manager (UEM). VMware has mentioned at the past few VMworlds that linked clones will be deprecated in the near future. When that happens they will also likely deprecate persistent disks.