HS transcripts / IB

Hello,

I wanted to ask of what importance are the high school grades received (or possibly awards and extracurriculars) before the age of 16 to some of the top universities (US or GB) universities. I am from a non-english speaking country and until year 10 I would get mostly bad grades. On the other hand I was on one of the 3 top secondary schools in my country.
Then in year 11 I would get just 3 Bs and then switch to an international school abroad for years 12 and 13 to do the IB.

Will they consider my application without much concern for the grades in my younger years if I get a good IB score (I have read a story of a girl here, who has been admitted to Harvard with a 6 5 4 on IB HL subjects)?
My predicted grades will most likely be very good and I have also made significant achievements in my CAS and supposedly will be able to write a good essay and get good recommendations.
So, do you think is it worth a try?

Thank you.