You can multiply coordinates by some small number I think, also here is an issue with painting over the landscape I have run into and found a solution, I hope this helps someone:
If you get black spots all over your terrain where some textures won’t load properly or if you are seeing blocky edges where textures should blend:
change all layers in your layer blend node in your landscape material to weight blend, that makes painting a landscape work as one would intuitively expect more or less.
The above solution works to reduce texture samples to minimum, but the problem with only being able to paint few layers per Component of a landscape actor persists, anyone know a solution? I am getting black spots where the layers blend with more than 3 on a single landscape component. Can I at least make the last applied layer override the lowest one somehow?