royal Marines or infantry

i’m 15 and 3 months so i can do my assessment for army in 4 months and navy in 6 months i’ve been waiting to join the army for a few years because i could join at 16 and go to harrogate but i just learned that i can also join the marines at 16 im not extremely fit i can run a mile in about 9 minutes and i can run at most 4 miles without stopping anyone got any advice on what i should do