Cleanup cache daily - only 15 days old

[krisp]

Instead of cleaning the whole cache every 15 days, it would be much better to cleanup cache daily for 15 days old content only.

With the present cache clearing strategy (every 15 days) a lot of cache younger than 15 days are deleted each time. With my suggestion only 15 days old cache is deleted and the younger cache is kept until it is 15 days old.