If this is the team that I think it is, then they *are* listening to the advice of their mentor, by having this test flight before SAC. Simply having their maiden flight at SAC would require less effort. Some teams do so, often by necessity because of limited launch opportunities (esp. international ones).
Also, regarding the advise of flying a smaller motor, please understand that this a German team flying in Germany. HPR motors are available in Europe, but not so much on a short notice. This is especially true for 75mm+ motors and even more so when only a fraction of propellants is suitable (high thrust ones in this case).
That being said, I think it's worthwhile to see if they can get the proper nozzle
in time and turn the motor into a research L1520T (unless @AeroTech
advises against that).