If both tachs are well pole and firing sequence adjusted to then revs are real world rpm. 1500 rpm are too much for idle, lower them to 1100-1200 at the most. Have an issue lowering them ? Can lower them to a point where engine doesn't die when shifting forward and maintains good idle just for this dry engine test.
Some issues :
-Induction tachs have erratic rpm lectures at idle, even ones when openning throttle.
-2 stroke engines doesn't like to idle at neutral for long time periods, will foul plugs.
-If with fouled plugs already engine will idle erratically or not even.
-2 stroke loves to rev as if you were stealing the combo.
-Running with more oil won't mess your carb settings nor produce higher revs, will just smoke more.
Bear in mind that if self oiling system is "not disconnected" and using pre mixed 50:1 fuel/oil ratio in tank you're not at 50:1 ratio, are slight under, will need to add what the system is self adding to the pre mixed 50:1 ratio, so fouling plug faster than at 50:1 while at idle.
Happy Boating