Is it possible to import class methods in ES2015

No, it is impossible to reference given values in class declarations.

However, class syntax is mostly syntactic sugar, and prototype inheritance works as always. You can simply put the method on the prototype object after the class definition:

import {myMethod} from './methodFile';
class MyClass {
    …
}
MyClass.prototype.myMethod = myMethod;

If your method needs to use super, you'll want to use the .toMethod method.