Loot refresh period and conditions

Does anyone know or have tested to try to figure how/when loot will refresh? For example the Elena garage loot everyone and their dog goes for lol. I'll drop by if I am in the area and see if I can snag an M2 and an AK 308 but 9 times out of 10 the loot is gone. Sometimes the door is wide open, sometimes its locked from both sides but the loot is gone. I got there last night, all the local enemies were present, had to fight my way to the door a bit, unlock it and found the crates open and loot gone. No big deal. I don't obsess over it but it makes me curious if anyone knows how often loot does get reset in places like this. We know the AI is about 15 minutes and there can't be (or shouldn't be lol) any players in the immediate area for it to happen but it sure seems like the loot has a much longer rate, which make sense but I wonder what it is.