Hi,
Are you collapsing with "Zero Elimination"? This will degrade the collapsing performance.
You should always run this compression jobs in the weekends in off-peak business hours.
Because it requires more BGD processes while compressing. I think you are trying to run in the business hours. That's why it is taking too long time.
While compressing, those cubes will be locked and will be unavailable for reporting. So it is always advisable to run in the weekends.
Please compress older than 7 days requests.
Regards,
Suman