It depends on what your goals are and how prepared you are now.
If you are prepared for the 1.4 exam and want to get certified in order to take further exams (like SCJD or SCWCD), then my opinion is to take the 1.4 exam and move on. On the other hand, if you're just starting your preparation now, and/or you have some need for the latest version, then 1.5 makes more sense.
"We're kind of on the level of crossword puzzle writers... And no one ever goes to them and gives them an award." ~Joe Strummer sscce.org
