I've seen this mentioned before but not sure what I should do in my case.

I just had my service A done after about 15 months with my 2019 c63s (delayed it due to COVID).

One of the items my SA went over with me after was my rear brakes. He said I should consider replacing them.

I've heard other owners had this mentioned to them as well, and from my understanding, the rear brakes get so much wear due to the ESP, not necessarily due to braking.

At first I was surprised he said my brakes were wearing out because I have carbon ceramics, but then I remembered reading that only applies to the fronts.

Anyways, I have CCBs so my car can still stop on a dime, and I'm about 15 months into a 36 month lease which I plan to get out of at about 24-30 months. So I have roughly another year +/- 3 months. Should I leave the rear brakes alone or replace?

Drive the car until you get a check brakes message on the dash, and if that happens it will be just rear pads that will need replacing which are an easy and cheap task you can do your self. Don't belive everything they tell you. Most of the time the dealers tell you and sell you crap just to make $$.

And, when you do get the brake-wear warning, you typically still have 3 mm of brake-pad remaining (out of the typical 10-14 mm on a new pad). That means that, things being equal, you should be able to safely run for at least another 15% of the mileage you've run up to that point on that set of pads.

BTW, in case you're wondering, even if you completely depleat your pads, you'll still have stopping power. Turns out that the metal pad-backing plate still offers plenty of friction when compressed against the rotor! I know this from having blown through my front pads on-track. Turns out that the sensor doesn't always work in high-temp conditions (looks like it completely disintegrated from the heat) so I got no warning ... well, other than the horrible grinding sound of metal-on-metal when the pad material completely disappeared. Needless to say, the rotors were badly scored during that event. Oops. $;-((

You're correct about the rear-brake wear being more to do with cruise/traction-control usage. Apparently, for "smoother operation" the brake-slowdown during cruise uses mostly the rear brakes. This gets really bad if you're using cruise on a highway route that has many steepish hills, since the cruise will end up using the rear brakes to maintain downhill speed (once it's too steep for engine-braking). I've gotten into the habit of disengaging cruise on downhill slopes.

I’m f&””ck tired keep hearing this. My SA told me the same thing. I Told him NO I’m gonna drive until the light come on. He try to scare me and said that I might not have brake once the light come on. I drove another 6k miles and the light still not on. I got a great deal of $650 for parts and labors from another dealer and do I decided to changed it.

When you bring your car in for service you should be getting an inspection sheet at the end where it says exactly how much brake pad is left front and rear. If your SA tells you you need to replace the pads, then take a look at what the technician actually measured. As others have said, the brake sensors typically trigger at about 3 mm. At that thickness you still have plenty of braking power for normal driving, but the pads won't be very good at dissipating heat due to a lack of material and will fade much quicker, so not recommended to go drive hard with a lot of hard braking.

Having said that, though, the front brakes do most of the hard braking. It is correct that the rear brakes do more work in modern cars. The EBD system (Electronic brakeforce distribution) initially favors the rear brakes and for light braking, because that reduces the typical nose dive during braking. By engaging the rear brakes first, the car stays flatter during braking. Also, for the FL, the rear brakes are used by AMG DYNAMICS to torque vector during cornering, so that's additional use of the brakes, however the rear brakes are barely used for traction control, because the 9-stage traction control in the S mostly controls traction by finely controlling engine torque and the locking differential, so the brakes don't need to be used to slow down spinning wheels. The rear brakes should last longer as a result. I was expecting mine to be worn much more than they were at my Service A. I still had about 75% left on the rear after 10k miles, and I regularly drive around in ESP Sport Handling and let the wheels spin a little bit.

As others have said, once the pads are worn you can just replace the pads as long as the rotors still have life on them. Every rotor has a minimum thickness stamped on the hat, so you can either measure it yourself or have a trusted mechanic measure it for you to see if they are good for another set of pads. I also recommend not to take your car to a dealer for brake service. Take it to an indy, or do it yourself and either way you can even order the parts yourself. I'm planning on aftermarket pads once mine are due and probably also upgrade the brake fluid.

After my 1 year Service A (april 2020) with 7,700 miles the SA informed me that the rear brakes were at 3mm and would need to be replaced soon.
Soon afterward at a different Dealership they confirmed the rear brakes were low at 3mm. The SM discounted the cost/labor on the rear brakes because of the low mileage but would not be covered under warranty. I had it done.

Photo below shows MB Brake/Tire Inspection report.

The PFL should use the rear brakes more, but I don't think it uses them as much as people think. Other cars with open differentials must use the brakes to slow down a single spinning wheel in order to transfer torque to the wheel with traction, but the C63S (FL or PFL) can simply lock the rear differential to transfer torque. The brakes only need to be used if both rear wheels lack traction. In that situation the FL can control the engine torque more gradually, finer and quicker, whereas the PFL may have to use the brakes for help and worst case cut engine power.