Sprint to olympic/standard

You should have no problem ramping up to the Oly distance.  You'll want to ramp up your swim workouts to include a main set of at least 1500 meters.  Maybe something like: 300-500 warmup, 1500-1800 main set, 200 cool down.  The main set could include a variety of distances but 50's-200's are a good way to go.  As you get closer to your race you'll want to prepare with some specificity. ie.  5x300, 3x500, etc.. A 1500 straight swim isn't necessary...just do the 300's or 500's with fairly short rest.