Your projections are off. With coaching and playing time at either level, both his bat and glove will continue to improve. It's tough to say whether i'd bring him up this season or wait another without knowing what the alternatives available are.
His defense in CF would be adequate this season, especially since (as dedalman mentioned) he will continue to improve his glove. Given good coaching, i'd expect 3-5 points easily. By next season, he'll be a 25-30 (+) play CF with adequate glove, good wheels, and a decent bat.
Patience is low though, so I'd try and hold onto him as long as possible, so might delay bringing him up.