At 15 years, you are old enough to get a part-time job! This would broaden your understanding of financial matters and help you to understand the sacrifice you are expecting from your parents.
Your lack of awareness of the intricacies of the various funding-options and the importance you place on having a specific instructor,say a lot about your youth,naivite and inexperience.
Spend some time reading the course-books such as the Trevor Thom series...Nav. will tie-in with your schoolwork maths/geometry/trig.
Technical will tie in with Physics...Human Performance -biology.
Weather-Geography.
Air-law is dreary ,dry but necessary r/t-well, save up (that job again!)
buy a hand-held tx/rx and listen in...learn the "patter", what it all means,how it relates.
You have a good few month's serious study ahead of you ,so why not use it to do the donkey work and put yourself in a first-class position to take advantage of those very expensive FLYING lessons.
RULE 1 NEVER,EVER pay up front UNLESS you can afford to lose what you have staked.
The "discount" or "bonus" rarely reflects the value of the risk...if it's too good to be true....that's because it IS.
Sorry, I've tried not to be negative and dampen your enthusiasm, but I get the impression that your family doesn't have a bucket of cash to indulge you in your passion,so just trying to make you step back and reassess your way forward. .