I think so.Do you have the ability to turn down the flow of the return pump?
I was able to get the Sicce to turn down. My tank has never been so quiet. I think I always had the COR turned up too much also. You'd never guess I've had this tank up for 10 years. I feel like a newby I've learned so much this week.So the old Neptune COR-15 you had was controllable up to 1500 gph. It may have been turned down to tune the flow in your tank not to overwhelm the overflow (I'm not super familiar with that model though).