P: 'Limit Preview Cache Size' taking too long to purge

To add more details (there's no edit button in here?) I've set my preview cache limit to 80GB in catalog settings, my ...Previews.lrdata is 130GB and I am rather constantly greeted by a rather annoying yellow warning sign that I should increase my preview cache to avoid having old previews deleted. 

I've tried optimizing, I've tried changing the size of the preview cache, nothing helps. The yellow sign keeps popping up and it feels like Lightroom is occasionally locking up for a few seconds because it tires to do something in the background. Maybe trying to delete preview files but failing, maybe not, I don't know. 

Hello, I am also investigating this issue and with V15 this issue persists. 

Just wasted an hour of my life with support on that. They are completely clueless on that feature and the person I worked with had the guts to close my browser so I could not rate the session with him.

So seems Adobe does not give ANYTHING about fixing their products any more.

Same here. Does Adobe have a bug for this? I even tested with a completely new catalog and still it seems to not be working at all. 

I get a message saying

Your preview cache is full. Increase the preview cache size in settings to prevent standard previews from purging. 

But it never does anything....

Add me to the "me too" group.  I changed it on day 1 of the new release, so well over a month ago.  My previews cache was just over 500GB at the time and I set the limit to 256GB.  Like others, I got the "allocated size is less than current size, purging soon" message.  I've been leaving LR running continuously since then, though restarting every 3-5 days.  My cache size has never gone down, and continues to increase.  I'm at 784GB now.  

I've currently the same situation, also "Allocated..." message. Preview file size about 180GB and set limit to 100GB. Waited for a day with LrC open. Also restarted computer and waited, but unfortunately preview filze still remains 180GB.

Definitely a bug. I have ~1tb of previews, setting the limit to 250gb I get the same message: "Allocated preview cache size is less than current cache size. Previews will be purged soon."

I first tried it on day one of release so it's been more than a month now... no change. The feature simply does not work.

Currently have a 97GB previews file. Each time I change the "Limit Preview Cache Size" option to below 97GB i'll get the message "Allocated preview cache size is less than current cache size. Previews will be purged soon."

Can this be moved to bugs or is this expected behavior?

Moved to discussions but I would say this is definitely a BUG...  software not working as described / intended.