If for some reason you must read the block device using a block size of 16K:
dd if=/mnt/nfs bs=16k | pv -L rate > /dev/sda Where rate is the maximum allowed amount of bytes per second to be transferred, or the maximum allowed amount of kibibytes, mibibytes, gibibytes, [...] per second to be transferred if K, M, G, [...] is specified.
However if you don't really have to read the file using a block size of 16K, just use pv, which can read block devices:
pv -L rate /mnt/nfs > /dev/sda