It is difficult to know exactly how long any given clickable should take to respawn but some of these timers are in practice too long. For example many of the item respawns are well over 5 minutes and each person in a group must wait. When you have 15,000 people waiting on an item to spawn for 5 minutes at a minimum of 52 DAYS assuming someone clicked on the item as soon as it spawned before those 15k people could get the item. 5*15000 = 75k minutes / 60 = 1250 hours / 24hrs = 52 days. While not all 15k people will try to do the quest there are more players than 15k and it is very unlikely that someone will be waiting to click on every item as soon as it spawns 24/7 for two months. Not every quest of this nature is required but plenty of them are part of longer chains with either pre-raid gear rewards or necessary to progress in the zone. Changing all items respawn timers to a maximum of one minute would reduce this down to 10 days for the server to hypothetically complete said quest. Realistically it wouldn't hurt anyone to reduce world spawn timers for clickables and considering the vast faction imbalance it could help alliance players having a hard time questing because of bottlenecks in spawn timers.
I dont really understand the logic behind your strange math, implying somehow 15k ppl would be attempting to loot the item or something, that made no sense.
Overall you are correct though. Most of the quest clickable items take atleast 2 - 3 minutes to respawn and theres really no reason for it. Dynamic respawn seems to only do anything for actual mobs. clickable respawn should be 1 minute at the most.
15k people is the server population ONLINE at any given time, the total number of players is higher. I don't personally have a que but guildies tell me the que times still have them in positions in the thousands during prime time meaning we likely have a total population of nearly 20k. Granted not every person will do every quest, but we can assume that a large portion of the total population (near 20k) will try to do those quests. It would be literally impossible for the quest to be completed server wide prior to that time. The other point I made was that the 52 days assumed that someone clicked on the item 24/7 for 52 days and instantly reset the timer; considering server downtime and peak hours the estimate of 52 days is even more generous.
I agree that clickable quest items take far too long to respawn, the same can be said for named quest mobs who also have an unreasonably long respawn timer.
A slightly related issue I noticed while leveling a nelf druid on medivh is that mobs have an unbelievably quick respawn rate, despite there being very, very few players in the zone. So there are several problems related to respawn rates that require attention.