I'm guessing that if you're already done preparing, you've been preparing for the 1.4 exam. The 1.4 exam covers only about 65% of what's on the 1.5 exam, so if you've been preparing for the 1.4 exam I don't think you'll be ready for the 1.5 because it has so many new and tricky topics!
My advice would be to delay your exam by a few weeks and study all the topics that are on the 1.5 that weren't on the 1.4 exam. At this point I think that the 1.5 exam is much more valuable than the 1.4 exam.
Spot false dilemmas now, ask me how!
(If you're not on the edge, you're taking up too much room.)
I think the the 1.5 exam has much more value in personal satisfaction but it doesn't make a huge difference in the job market. Now that there is more material available for studying (e.g. Berts book is hitting shelves now) studying for the 1.5 exam is much easier. In the end it depends on your view, do you want something that will look more up to date for longer, but on the downside of being a little harder to study for, or do you take the view "They just want someone to be Java Certified and won't look much further beyond that"