It is hard to follow because the numbers change on draft day with the bidding system, but I don't completely make sense of it.
I'll go with draft guru.
20 plus 38 from Fremantle for H.Bennell plus 27. Then later 56 plus 2016 Future pick Round 2 to
Gold Coast for picks for 35 and 61 to Fremantle. (On draft day our picks were 27, 38, 55 and 61).
www.draftguru.com.au/years/2015 Handy historical reference site nevertheless.
Edit: So 20 was 16, 27 was 22, and I'm not sure about the difference between giving up 38 and getting 35 back later in the second part of the trade, but it seems to be much the same pick)