I don't think the Eastern Beaver kit is required for the Roadster models, 2010 and up (needs confirmation) since Triumph performed an upgrade to the headlight wiring sometime around then. Your 2015 Roadster should be fine.
If you replace the standard halogen bulbs with LED bulbs or full blown LED sealed beams, you would reduce the power requirements dramatically. You probably wouldn't need to upgrade the ignition switch by doing this on the earlier models. Even though I owned a updated 2012 Roadster, I performed my own upgrade.. see this thread
Home Made EB headlight relay harness