Fast path sends data pretty much as it receives it. There is less latency (ideal for gaming and video steaming) but far more prone to errors.
Interleaved changes the order of the data so that if you get a "hit" on the line it affects a few bits from different parts of the original data stream rather than knocking out one big chunk at one location in the original stream. Error recovery is much better but you pay the price by higher latency.
Fast path is a bit like a deck of cards sorted in order. Interleaved is a shuffled deck.
Pull out 4 cards in one location from the deck. The sorted deck could well loose all cards of the same value, the shuffled one will be random cards.
Let us know should you need further assistance.