Interpretative is slightly more common than interpretive in 21st-century British publications. Everywhere else, including in the U.S., Canada, and Australia, the shorter form is preferred.
Some people consider interpretive etymologically incorrect because the Latin stem is interpretat-, not interpret-. Plus, there is plenty of precedent for using the longer form—for example, English speakers favor argumentative, exploitative, and authoritative over their shorter variants. But English is not always consistent in its word constructions, and these things are usually decided by popular usage rather than logic.
In British publications, we find about two instances of interpretative for every interpretive. These publications, for instance, favor the longer form:
The technical and interpretative problems for the performer, who essentially has to treat each hand independently, are immense. [Guardian]
These performances of two landmark violin concertos. demonstrate a remarkable meeting of interpretative minds. [Telegraph]
He contents himself with printing his own interviews with his 25 world changers. rather than writing interpretative essays. [Economist]
Elsewhere, interpretive is more common. Here are a few examples of the word in action:
Other interpretive choices were even more puzzling, like her dreamy, almost languid rendition of the Gigue. [New York Times]
Perhaps the interpretive traditions attached to Don Giovanni are a bell that can’t be unrung. [Globe and Mail]
Regional pioneer Wynns Coonawarra Estate. has opened an interpretive centre that takes wine enthusiasts on an interactive and educational journey. [Sydney Morning Herald]