As much as everyone, including me, has appreciated Ortiz over the years I do not think that the Sox should financially enter into anything more than a one year contract at a time with him.
He is at least 38 years old and is very much a risk every single year to fall off the face of the earth performance-wise. $15-17 million a year as long as he does well is fine, but the thought of paying him that much to maybe not even be able to play is too large of a gamble with the team's annual salary limits.
Remember how so many pieople were upset with Schilling getting 8M for the year that you was unable to pitch. Ortiz is going to have a contract that will be twice as big.