Ah, well you may want an FInterp after all, but may not need it or if you do will need to change how you are doing things (depending on your setup, and assuming I am actually understanding what you want now).
Assuming a 2D setup, if your ship is a Character you can abuse the CMC, even though a ship isn’t very character like (I do this with non-humanoid robots), turn off use controller rotation, turn on use controller desired rotation and set a desired rotation rate (last component is yaw).
No sure if floating pawn movement has analogs to that, but if your ship is a pawn and you are controlling everything ‘manually’, you will actually want FInterp, but using the axis values from mouse events will not be helpful, you will need to get the mouse location, subtract ship location and build a rotator from that, which will contain your target yaw for the FInterp (which is in Tick), something like:
Let us know how you go, or if I should ‘expand’ on anything above 