The 2015 coils are vastly superior. However they aren't compatible with the plugs on the 2013/14 harness so to update the coil packs, one must also update the harness. This assumes a simple adapter from a 2015 coil to 2013 harness does not exist (it didn't when I updated mine). 3 Racing seasons, not a single failed coil.

I recently installed a 2015 motor into a 2011 forester and spliced in the later coils to the original harness. Not too involved.

I was curious about this, but not sure how sensitive the ignition system is in the BRZ under high temp/high load with spliced ignition wiring. Arguably a situation few Foresters will ever see.
There are adapters now (which I can't find anything negative about). The company that makes the adapters also sells pre-terminated pigtails. This option is really tempting; wire splicing is something I'm plenty comfortable with.

https://www.icefabrication.com/produ...grade-to-2015/

https://iwireusa.com/products/ignition-coil-plug-e


Regarding the harness itself, I'm finding some confusion with PNs. The TSB states the 2013 and 2014 use different update harness PNs, but the harness PNs for the 2015 and 2016 model years are both 24020AG080, same as the 2014 in the TSB. Is it not compatible with the 2013?

https://static.nhtsa.gov/odi/tsbs/20...31587-9999.pdf