ARC LS15: did they ever use Mundorf MCaps on it ?

If you are truly interested in buying this preamp your best solution is to have the seller send it to Audio Research to be checked out. Once Audio Research has given it their approval they can forward the preamp to you after you have paid the seller. I have done this several times with great success. It relieves the seller of liability and the buyer knows he is getting a unit that is working properly.

so, the answer is: no, ARC never used Mundorfs on LS15, as I thought.
I am in Europe, and as some said I'd better buy an LS25 or some Ref than send the LS15 to USA and back, paying ARC's intervention in the middle... ;)

"ARC will never send anything back out with mods."

Some years ago they repaired my PH-2 containing numerous DIY cap substitutions. My caps were left in place.

Personally I wouldn't worry about the Mundorf Supreme substitution. IOW of today there are better caps available than either of these.

ClarityCap OEM Sales

OP says M-caps not M Supreme if I recall correctly.
As we can see there are several members here who belong to the school of die hard "keep it stock". I respect that but I personally am a "respect the mods as long as its done right (get close up pics), as long as you research the sonic character as the components replaced."