That can be qualified: They are optimised to act as short-term backups that will be accessed perhaps just once (if at all) and then deleted.
But because of the lack of alternatives they often get used in other situations where they are indeed 'slow' by design.
An alternative LVM "thin provisioning" snapshot implementation is now available that is optimised for having many long-term snapshots of the same volumes, sharing data between them where they can. Example:
# Set aside 10GB for a pool of thin logical volumes (thin_pool1) in vg1
# and create a thin volume called thin_vol1 that purports to be 2GB in size
lvcreate -T -L10G vg1/thin_pool1 -V2G --name thin_vol1
# Put some data on vg1/thin_vol1
# Create a thin snapshot of vg1/thin_vol1
lvcreate -s vg1/thin_vol1 --name thin_snapshot1
Commands that allow the creation of thin snapshots of existing (non-thin) logical volumes are under development.