Running 100 iterations, decrypting on FST-01G (Cortex-M3 @ 72MHz), it's like:

gpg: encrypted with cv448 key, ID F6FA616F8E4378B9, created 2021-03-09
      "Kunisada Chu <chuji@gniibe.org>"

real    0m34.189s
user    0m2.512s
sys 0m0.387s
gniibe@iwagami:~/work/gnuk/gnuk/src$ 

That is, 0.34189 second for a single decryption process.

It's good enough for me.