AFAIK in markets where there was a 2015 MY C63, it was the new W205 chassis sedan with the 4L biturbo. The 507 was only marketed and sold as a 2014 MY.

Yup. All M156 engines made after a certain date in 2011 have the updates lifters from the SLS.

Ugh... this is the very symptom and issue that has been discussed ad nauseum here and applies to all other engines that use hydraulic lifters / buckets. The valve lifters are worn and can't keep the pressure when you shut off the engine and they are under an open valve and the valve spring is pressing down. After you start the engine it takes a number of minutes until they finally build up enough pressure to fully expand the lifter so that the valve lash is back to zero. On a car that has the updated SLS lifters from the factory that don't bleed down and furthermore only has 30K km on the clock to boot, unless that car has been sitting for MONTHS that much valve lash definitely indicates that all is not well under the hood. It can be intermittent because the worn lifter(s) will not always end up under an open valve when you turn off the motor.

I believe that the W204 C63 507 AMG Coupe was available as a 2015 model along with the new C63 and C63S W205 AMG sedans.

Thats right. Mine is a 2015 C63 AMG 507. Bought from MB of Portsmouth NH.

I'm in windham area !

Hahah Nice! So i actually live in MA, but know the owner of the dealership. The Kaplan Group which also owns Range Rover/Jag of Natick MA.
If you are ever looking for a ride, look me up, and i will introduce you to them!

Cool - I didn't know that. Thank you!

Wow that ticking is very loud!