Correct Wiring
I assume you have a single relay harness. If so, only 1 capacitor is needed.
You must FIRST plug one of the original vehicle headlight plugs into a capacitor. I found the plug on the passenger side worked best.
Then plug the mating end of the harness into the other end of the capacitor.
Note: The vehicles driver side headlight plug is no longer used so tape the end of it and wire tie or tape it where it can't bounce around or short against anything.
Your remaining two relay harness plugs connect to your ballasts.
The "battery" wire feeding the relay harness (usually red) can be connected to the unused stud on the vehicles fuse block on the passenger side. I bought an M8x1.25 nut and matching size ring terminal to attach it.
You need to find a good place to attach the "ground" lead from the harness (usually black) to the engine block or other suitable location.
I used an H11 INNOVITED 55 watt 5,000K slimline kit on one vehicle and an OPT7 55 watt 6,000K slimline kit on another vehicle. Both kits worked very well and I was able to mount their passenger side ballast on the core support rather than under or behind the air cleaner box. Both brands appear to be quality kits and are very affordable at about $70 on Ebay.
Like most brands, different color bulbs are offered but after trying two I preferred the 5,000K color for their greater light output and whiter light. The 6,000K give off a noticeably blue light. For reference O.E.M HID lights are about 4,300K. The greater light output of the 55 watt version works very well with the 2015's projector lenses due to their abrupt upper cut off so the extra light is directed downward and oncoming drivers don't get blinded.
You definitely need the optional relay harness and one capacitor to make HID's work on the 2015 vehicles. Capacitors usually come only as a pair but they are cheap. The capacitor smooths out the PWM signal and the relay supplies full power during the DRL function.
OPTIONAL: When replacing the air box, I removed the restrictive silencer that snaps into the outside of the air box to allow for better breathing. I used a 2" thick by 1" wide by about 30" long foam strip left over from a window A/C to replace the original thin foam seal from the air box to the inner fender. Two of the original 1" foam seals doubled would probably work as well. The engine now sounds more "throaty" and not too loud. Another nice improvement I think.