My dentist said i need braces and im nervous about how long it will take please help?

ok so my canines are like all the way up and the teeth next to the pointy ones are a little crooked and my two front teeth are ****** a lil but u cant reall tell ..im 15 and my dentist waited soo late to give me braces and i dont want to have them for a long time so do you tik i will only need them for 1 in a half years?and no i dont think i could get invisables...i would show a picture but idk how