Also tested in UE 4.15.3
Problem: The Editor crashes on copy and pasting a landscape spline over to another Level.
Always remember to select the right Level and Landscape in the Landscape Manager. Would be nice if the Manager would select that for me depending on the selected objects… maybe later for a feature request 
First way
- Save The Level (L1) you are working in - it will be the Master Level
- Create a new empty level (L2) and Parent it to the persistent level
- Create 2 Landscapes (LS1 and LS2)
- Add a Landscapespline to LS1 (With Edit Spline tool: strg + left klick on Landscape)
- Select a Splinesegment and copy it with ctrl+C
- Select LS2 in the Landscape editor
- Paste the Spline with ctr+V and leave Lanscape Manager
- Try moving LS2 to L2 (Select LS2, right klick on L2 in Level outliner and select ‘Move selected Actors to Level’)
Crash
Another way
- (Recreate first 3 steps from above)
- Move LS2 to L2 (Select LS2, right klick on L1 in Level outliner and select ‘Move selected Actors to Level’)
- Add a Landscapespline to LS1 (strg + left klick on Landscape)
- select all Spline segments with the Button in the details Panel (otherwise it won’t copy) and copy it with ctrl+C
- Doubbleclick on L2 in the level outliner and select LS2 in the Landscape Editor to paste the spline with ctrl+V (Visually nothing happens)
- Save and close the Project.
Now it should crash on opening the Map. If L1 is the standard level to open on the Project, L2 has to be removed manually in the project folder, to be able to open the project again.
If LS2 is a Copy of LS1, it crashes in the process of pasting the Spline onto LS2 in L2