Colbert actually said that there were as many as 19 they liked. I think that may be a little telling. If they get to pick 15 and there were some surprises early, meaning 5-6 players are there they like, they may slide down. If not, expect them to use the 15th pick.
Also, Tomlin and Colbert stated that they do not expect a starter this year, hope they can contribute on special teams or sub-packages, but they are just young talented guys that have to prove they have the maturity, mental makeup, and other aspects to improve and help the team.