i dont think the excise office verifies the chasis, you can just check the file of the car there to ensure that the original purchase invoice and other documents are there and that the registration number does pertain to the same car. the office is in F-8 markaz.
For chasis verficiation, there is a laboratory test, i dont know done from where.
15 only checks that there is no report against the car, i.e. stolen or involved in some malicious activity.