Also we know that there are at least two prototypes '1601' & '1603' ... and by the way since it is based on a proven airframe at least aerodynamic testing can be cut considerably.
Deino
That is correct, with the number designations changing from J-11- J-15, J-15s, J-16, the novice might assume that each of these designators were for a completely different aircraft, and they absolutely are not, but are all variants of the SU-27, so these pre-production aircraft would be more accurately designated as "test articles" rather than prototypes such as the J-20 proto-types which are currently being developed. Even the addition of canards on the J-15, would simply qualify it as another "variant" say the F-15c as oppose to the F-15e.
Now granted that there are electrical, plumbing, structural changes that require a great deal of engineering and fabrication, not to mention "purpose driven" avionics changes, in the US that would be handled as an STC, or "supplemental type certificate" accompanied by a few pages of changes in the Dash-1 and the aircraft log book reflecting operating changes, and weight and balance, and a flight test program to make sure you didn't acquire any "bad habits".
These observations are born out by the batch production, as we are able to re-tool for whichever version we need to produce next, as I continue to state= "A Flanker, is a Flanker, is a Flanker", and I have little doubt the Chinese birds are likely built to a more rigid standard. The Mig-29s I have been close to, seemed rather "crude", and the Indians are complaining that the Pak-Fa prototypes are a little rough as well???? so, I love the Chinese Flankers, and I like the J-15 the best of all, they are each going to be very capable aircraft.