IV Strategy

15 att, High level already

Atk is separate in the CP formula, while Defense and Stamina are being multiplied. In order to get a higher number for this product, you want balanced stats. To achieve this, you can for example choose to power high IV of low base stats.

Umbreon's lowest statt is atk ;-)

I usually look for a high attack. I also prefer HP over Def because lower Def actually makes you build energy faster from defenders' attacks, increasing your DPS. (Or at least that is my understanding).

I also agree that it is generally better to have a high IV for the mon's weakest stat. For example, don't power up a snorlax with a 10 attack.