I have been told this is high, and that it might be due to the interleaving.
It's a bit high, but not excessively so, and if interleaving is still present on your line then some of it is undoubtedly due to that.
I think 5km's estimate of a 10mSec improvement may be a bit low, but there's no easy way to be sure without getting it switched off and looking at the result!
Be aware that interleaving does
provide greater tolerance to some types of interference on the line, and that removing it might (but equally might not) lead to an increased frequency of interruptions due to re-syncs. If this happens too often on a BT line the dynamic line management systems will usually put interleaving back automatically.
It probably won't greatly improve your speed (certainly not in proportion to the latency improvement), and unless you're a gamer and thus ping times are important to you, I'd be inclined to leave it alone.