so hard to say based on your info. Go to 3J's sticky thread, get your BMR/TDEE then it would be a lot easier to assess. Im doubtful you 18% at 5' 11" 275 but might be.
im 5' 10" and when im at 10% im about 175, i know its not an exact science and people vary but when i started cutting i was 195 and about 14%