I think it depends on what you are looking for.
Quite possible that employers might not know the difference between 1.4 and 1.5. So if you are just looking out to put SCJP on your resume, 1.4 is easy and works well too.
However, with the release of 1.6, 1.4 would be a little outdated. 1.5 has many new features. Also down the line, may be your employer upgrades to 1.5. And to top it all, its the satisfaction of learning. In this case, 1.5 makes sense.
At the end of the day, its your call
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