@Grace T. and
@RandomSoccerFan have good points. Private's and individual sessions really pay off over the long term where those skills can be taken and applied at team training consistently. Short term, improvement will be incremental. U15 is also an age where players need to identify the gaps in their game and be intentional about improvements. If fundamentals technical skills are lacking at this age, chances of catching up are slim. However if technicals are strong and it's purely a late developer scenario, biology will hopefully even things out by U17.
What level does your player currently play? High School soccer is so sporadic in terms of ability level. Unless they are attending one of the CIF Div 1 or high level Div 2 schools, a mid-level flight 1 team should generally be enough for the Freshman or even JV teams in SD. I know a handful of rec players that made the JV teams at a few schools, but they will be hard pressed to make Varsity as juniors.