Other: Does Clear-Com provide the HS-15 headset with a 4-pin XLR connector?

Yes, the HS-15 single muff and HS-15D dual muff electrec headsets are available with 4-pin XLR-F connectors. 
Description from 2014 accessories brochure:
HS15-4F Headset:
Ultra comfortable, single-ear, lightweight headset with an electret noise-cancelling microphone.  4-pin XLR female.
Note: Compatible with HME PRO850, Tempest,
CellCom/FreeSpeak, V-Series panels and RS-700 Series beltpacks.
HS15D-4F Headset:
Ultra comfortable, dual-ear, lightweight headset with an electret noise-cancelling microphone.  4-pin XLR female.
Note: Compatible with HME PRO850, Tempest,
CellCom/FreeSpeak, V-Series panels and RS-700 Series beltpacks.