I've been using WTBackup on my laptop a couple of development servers as well as a couple of production servers. It works very well.
One of the reasons the backup might be slow is the time it takes to create the zip file at the end. If you are doing a full vault backup and creating a zip file of it, it will be slow. I would rather suggest not backup up the vaults. The vaults should be backed up using the normal file system backup (tape drive) as it is usually a large amount of data. It could also be that you are not using vaults and all the data is sitting in the database BLOB.