Here is a simple word study that attempts to bring some clarity to what, in English, seems like a contradiction between Jesus and Paul:
"Do not think I came to abolish [καταλῦσαι (katalusai)] the law or the prophets..." Mt. 5:17
So, Jesus said he would not καταλῦσαι. Remember that.
"[Christ Jesus] himself is our peace, who has made the two one and has destroyed the barrier, the dividing wall of hostility, by abolishing [καταργησας (katarghsav)] in his flesh the law..." Eph 2:15
So, Paul said Jesus would/did καταργησας.
Jesus and Paul said different things
'καταργησας' is not the same word as 'καταλῦσαι.' Sure, they start the same: 'kata.' But that doesn't mean they mean the same thing (think 'cataract' and 'catapult'). Post-'kata' we see 'arghsav' (Paul) and 'lusai' (Jesus). Digging into etymology and word construction can, a veces, mislead/prove useless (think 'aract' and 'pult'), but might help in this case.
'Arghsav' prob. has 'argeo' as its root: meaning "to be idle, inactive, to linger, delay." 'Lusai' prob. has 'luo' as its root: meaning "to loosen, undo or dissolve anything bound, tied or compacted together."
So, maybe Paul's word is softer that Jesus' word. Maybe, if you asked Jesus for clarification, he might say that, while he won't καταλῦσαι, he'd be totally down with καταργησας.
καταλῦσαι appears again in Matthew's Gospel, in 26:61 where we hear: "This man said, 'I am able to destroy [καταλῦσαι (katalusai)] the temple of God". The One who would not καταλῦσαι the law or the prophets was accused of threatening to καταλῦσαι the Temple (and this generated momentum behind his execution). καταλῦσαι seems like a strong word.