I don't recall actually ever listened to any part 15 military stations that I recall, but they have certainly existed for decades (ever since the 1940s) at numerous bases, most commonly carrier-current AM. Military documentations as late as the 1990s (perhaps even later) actually specifically address the operation of part 15 AM on bases.
But no, I've never actually listened to one.. not knowingly anyway.
Google AI provides a good overview of the first military part 15 AM network, which were at numerous locacations around the world at the time. I was known as "The Star Spangled Network:
The Star-Spangled Network was a USO radio network established in 1941 that predated the Armed Forces Radio Service (AFRS) by several months to broadcast entertainment and morale-boosting content to military personnel. It used wired radio systems, where studios in USO clubs broadcast directly to radios on nearby military bases, bypassing traditional radio frequencies. This network was part of early efforts to support American troops during World War II and was a precursor to the later, more comprehensive, Armed Forces Radio Service (AFRS).