If you already have an EAD, for instance as a derivative beneficiary, you only need to fulfill the State licensing requirements.
I cannot think of any reason the law would be different for PT's in this respect. You can only carry the priority date (if your I-1485 was not filed more than 180 days ago). You will have to refile the I-140 with the new employer. Read my blog.
PT's and RN's are both exempt from filing labor cert, but the time for their green card processing is still tied to the time it takes for people from the country of their birth. An India-born PT will wait the same time in EB-3 category as any other India-born EB-3 applicant.