Itachi suffers from backlash using 1 amaterasu.He can barely hold his Susano'o for long.
Fallacies
Itachi used two amas after sustaining backlash from tsukuyomi (during sasuke fight), that was what injured him.
He also used two tsukuyomis before using ama to escape in part 1
& as for susanoo, he maintained it right up until death. Honestly its apparent that uchiha have powerful chakra, therefore powerful jutsus. Susanoo is a powerful jutsu but when was it ever stated that susanoo drains massive amounts of chakra? it wasnt, susanoo can take as much as a simple rasengan to make, the only problem is the drain on his actual lifeforce which can be avoided or drastically reduced if he uses susanoo ribcage with an arm/yata.
Itachi isnt going all out, he doesnt need to (unlike during sasuke's battle). Susanoo will be used in the
most dire of situations, & even then he wont need the full thing when yata can do just as much defensively.
So in conclusion itachi wins this, jiraiya will have to keep up with itachi's handseals, his shunshin, his ama, his tsykuyomi, & his ephemeral all without the use of his hands in order to prep SM. This is mid diff at most..