Is it normal for a ~2TB drive removal to take days?

I have a nearly full raid 1 pool that I'm migrating from 3 2TB disks to 2 8TB disks. I used `btrfs device replace` to change out the first 2 disks, which each took about 4.5 hours. Then I started `btrfs device delete` on the remaining 2TB drive. That was 2 days ago and it's still going. Iotop shows btrfs writing at anywhere between 2-3K/s to 20-30M/s. I have not yet expanded the filesystem, I wanted to wait until the old drives were all removed first.

$ mount | grep bucket

/dev/sdc1 on /bucket type btrfs (rw,noatime,compress=zstd:3,space_cache,subvolid=5,subvol=/)

$ sudo btrfs filesystem usage /bucket -T
[sudo] password for robert:
Overall:
    Device size:		  3.64TiB
    Device allocated:		  4.90TiB
    Device unallocated:		 -1.26TiB
    Device missing:		    0.00B
    Used:			  4.90TiB
    Free (estimated):		  8.00EiB	(min: 8.00EiB)
    Data ratio:			     2.00
    Metadata ratio:		     2.00
    Global reserve:		512.00MiB	(used: 0.00B)

             Data    Metadata System
Id Path      RAID1   RAID1    RAID1     Unallocated
-- --------- ------- -------- --------- -----------
 1 /dev/sdc1 1.82TiB  2.00GiB         -     5.46TiB
 2 /dev/sda1 1.26TiB  2.00GiB   8.00MiB   572.91GiB
 3 /dev/sdd1 1.81TiB  4.00GiB   8.00MiB     5.46TiB
-- --------- ------- -------- --------- -----------
   Total     2.44TiB  4.00GiB   8.00MiB    11.48TiB
   Used      2.44TiB  3.18GiB 384.00KiB

Is there a way to check the progress? Some way to speed this up?

Thanks for the help!