I don't have the PHEV version of the Nero, just the standard EX Hybrid. We do I believe share a common ICE system and mine doesn't act like yours. I can get my car to start in just battery mode depending on the residual charge amount left on the HV-Battery in the front. However, if you do push the acceleration, or when the battery drops below the 50% mark, the motor will kick in and runs at full tilt (30L/100km) for about 45 seconds, then drops down to (20L/100km) for about 2 minutes more. Then will either shut off, or run doing top-up power depending on how fast you are driving or the grade of the road. If you slightly bump up the speed by 5km/h and then back off the accelerator, the motor will shut off and you can force it to drive in EV mode until the battery drops to 1 pip below the 50% mark.
All that said, my owners manual says that we need to change the oil every 6000km for extreem condition (that lists if the weather drops below freezing, or there is snow, or driving on gravel ... rather BS list) or 12,000km or 1 year. I guess that translates to your 7500 miles. Now the instruction manual doesn't say anything about having to use Synthetic Oil that I plan on doing, and I found that doing it myself costs about the same for Synthetic as paying for the dealership to do an oilchange using just regular oil.