I really cant see an anemone of any species thriving in a 15 gallon aquarium. Anemones need a fairly stable salinity, ph
, calcium, etc, etc not to mention nearly perfect water that is somewhat near free of nitrates. Keeping such values in perfect adjustment in a mere 15 gallons of water seems almost impossible to me since daily there are bound to be fluctuations. While I have heard of BTA's doing alright in smaller tanks this is not without risk since if the Anemone where to die the heavy pollution may be enough to kill all the inhabitants of such a small tank.
Also like Salttanker said a tank with 6 months or more maturity is needed before keeping an anemone - in that size tank I would give it some careful thought.