As soon as the user comes into battle, it transforms into its opponent. Imposter copies the target's appearance, cry, moves (which all have 5 PP), Ability, stats (except HP), stat changes (but not stat multipliers such as with Choice Specs), weight, and Mega Evolution or form (regardless of held item).
~ Bulbapedia
When Ditto transforms, it copies its opponents exact stats. All of Ditto's stats after transformation are irrelevant, except for HP. Yours has a perfect HP IV. I say it's worth keeping if you're using it for battling. For breeding, however, 5IV-6IV Dittos are much better.
