The only way to know for sure is to actually shoot 5 shot groups at different ranges. The most critical to check at 5 and 10m because the pellet is rising steeply. Do this with the pellet you have chosen and redo it if you change. Gamo pellets are not the best in my own personal experience. I've found that sitting is the best position to do trajectory tests but you could find most consistent grouping from a rest or sandbag. Use a bag of sand or soil as a backstop if doing it in your back yard. Also consider your firing zone and neighbors / housemates so they don't get alarmed.
There is an app for phones called chairgun which is free and will calculate trajectory pretty well. It has an airgun pellet library. You could just put in the advertised velocity and choose a pellet similar to yours and it will put shots on the paper for you. Your gun will be 10 - 20mm low at 30m if sighted for 15. You'll probably find you can use a 20 or 25 m zero and run it shooting 5 - 10mm low at 15m. 30m is likely to be an outside extreme range to hit a rabbit's kill zone.
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