'If' you walk to the boat dock at DHS and get right on a boat, then yes, it will be about 15 mins to YC/BC. But, if there is no boat coming in (that you can see), or if the boat is leaving the area, then you need to add at least another 15 mins to that time. You stand a much better chance of it taking a total of about 25-30 mins to get to BC from DHS if you take the boat.
If you walk, it will be 15 mins...period. I would walk, taking the sidewalk that runs beside the canal. When you get to the back of BW, behind Jellyrolls, go left, up and then to the right, over the bridge. You are now walking towards YC. You can enter at YC or keep walking along the boardwalk area until you get to the entrance to BC...either way will work.