Again, I know that Doom has the bands of Cyttorrak, but still, he's only passing through Ultron with magic bfr. 15 seconds is pretty much just the time to shield up, Ultron can, at the very least, control a few robots and bring them to the battlefield, distracting Doom and minimizing his chances of winning.
Doom autowins is the most rehearsed argument when he appears, in this battle his armor may as well get hacked, he may as well get ionic explosion bashed for all his worth, Ultron can hurt and ko Thor and has done so on occasion. Physically and magically prepped Doom couldn't beat Thor -although he was interrupted before the Destroyer Armor was finished, but still-.
Bottomline, Doom needs to bring very good moves to bring Ultron down, I'm not even sure he can summon the Mindless ones since he prepped in the past wtih Morgana to send them against the Avengers. Bands are fine, but Namor broke incomplete bands, Ultron should be able to do so.
If you got magic-bfr that may actually work against Ultron, then Doom can wins. Otherwise this is gonna be a painful combat for him.