Your copy/paste method is doing just that. When you back up using Lightroom it optimizes the catalog and checks it for referential integrity. But 5 min. does seem to be a little bit long.
I've turned off optimize and integrity check and I'm getting 5 minutes... compared to 30 seconds copy/ paste
I guess you will have to see if someone else has an answer. I don't experience that sort of problem on my system, and don't have any suggestions. What OS are you using? How much RAM? A few system specs might help.
I experienced the same issue on windows 7 x64 and now on windows 8.1 x64.
Intel I7 3770K
My catalog is large with about 450,000 photos, but my performance in the rest of LR has been just fine. It's just really surprising that no-one else has this issue since I've experienced since I started using LR a few years ago.
Photos in my catalog are hosted on a variety of drives- raid 0 for my work in progress, and several different disconnected drives that host the remainder of the pictures). On of the disconnected drives is a NAS that I have mapped with a windows drive letter... I have my unconfirmed suspicions that LR disliked NAS drives. It would be nice to know from adobe if LR is actually doing something important during backup or the copy paste method is just as good.
I would guess that LR is copying over the database structure, but not doing extensive tests on it before making the copy. (That is what the check integrity is for). If LR crashes making the backup, then it might indicate a corrupt database, which you would never know about from copying it. Of course, if it doesn't crash making the backup that is no guarantee that the database is consistent.
Me, I would close the database, make the copy and archive it, then open the database and let LR test it and optimize it after I go home for the night. Then you'll have a nice, optimized and hopefully bug-free database each morning.
I also have had issues with slow catalog backup's ever since LR 4, I have only used it since V3.6 but it has degraded noticeably since then.
In fact I have now reverted to using Project type catalog's of no more than 2-3K images to get around the issue. I guess it is unfair to compare LR performance to other RAW editirs with DAM's but it will come up.
My findings are listed under a Problem on Photoshop.com at: Catalog Backup noticeably degraded since the release of Lightroom 5 but unfortunately no input from Adobe as yet.
As of LR 5.6 This is finally fixed (at least for me). Backup through LR now takes similar amount of time as a simple copy-paste.