Yes I have a stages power meter on one bike and the other has garmin xc rally pedals. There is definitely a 10-15 watt difference, I think it’s mainly due too the power being measured at your foot compared to the arm.
I assume garmin power numbers would be more accurate than a crank arm based power meter. I’m not sure but I have seen the same difference as you have.
Edit: I have done a ftp test using both at the same time and it was 12 watt difference.