Other than using the software renderer, which seems unlikely as it would be very obvious and also unnecessary on modern hardware, you should not see any performance drop for the same code.
Code can detect which profile it’s running under and run different code, and Starling does in a few places, but generally it should run faster under a more modern profile, as it offers new and improved ways to do things. Might be worth looking through the Starling code for any dependencies on the profile that your app might be affected by.
Apart from that it might be something particular to your setup. E.g. different profiles might be associated with different device drivers, such as different versions of DirectX, some of which are less optimised than others. Test it on other platforms and devices; if it is only on your PC you can probably ignore it.