To validate a model, can I compare the optimal conditions with that of the same model with 6 new runs added?

[#1]

Here are the optimal conditions for the model comprised of 15 Box Behnken design runs with standard least squares. 

HotellingGnu652_2-1679684614317.png

The optimal conditions for the model comprised of the same 15 Box Behnken design runs + 6 new runs, yield nearly the same optimal conditions with a slightly lower defect rate to fall within the spec limits. 

HotellingGnu652_3-1679684621834.png

Could it be statistically justifiable to compare the optimal conditions of these two models, with a T-test or any other test, as a means of model validation for the standard least squares platform? All opinions are welcome!

[#2]

Your approach might work. You might instead apply the original interval for the predicted mean response [12.1783, 39.7935] as the acceptable range in a test of equivalence with just the new, independent 6 runs. Us half the interval length for the test. See the JMP Help about Test Equivalence with the Distribution platform.