1M baud Optiboot for mighty1284p

[retrolefty]

The baud rates for an AVR processor clocked at 16 MHz are...

  ...
   333333
   500000
   666666
  1000000
  2000000

There is nothing close to 1.2 M or 1.5 M.

Looks like some kind of Satanic number sequence to me, be afraid, very afraid.