A healthy teenager messing around with doctors and blood tests seems in itself not healthy (a contradiction?) .
Don't go in to this super obsessive pursuit of 'health' - it can lead you the opposite of what you want and trying to achieve (it can actually lead to bad mental and physical health).
“Avoid grains and process food/drink, sugar junk food, takeaways” - OK
“Eat meat, veg, eggs, tubers, fruit and full fat dairy etc ( if you can take dairy)” - OK
"Good sleep and exercise" - OK
For you as a healthy growing 15yo - DONT DO : Ketosis, calorie limiting, I.F., carb (veg/tubers) avoidance, trying too hard to eat super-high fat diet, excessive exercise, extreme low body-fat %, pursuit of diet/health perfection, blood tests and doctors etc etc etc (these is NOT a healthy pursuit for you now IMO).
Think of it like an apprenticeship of good health/diet – you wont be and expert overnight. It will literally take you about four years of steady study and practice, slowly over time things will “fall into place”, some years down the track you may consider yourself a practising ‘expert’ (but you never stop learning) – then you have the rest of your life to practice and improve on it if you want.