At the age of 15, boys are "interested' in a lot of things. This doesn't mean he will be interested in aviation in a year or two. I would be far more impressed if the kid went to some local FBOs, and local businesses and offered to do any kind of work for them for some money, put up some signs saying he will wash airplanes and do whatever for the owners, get a part-time job and save his money, save the money from birthdays, Christmas etc., that he might get along the way, sell a few things that he doesn't need to schoolmates, offer to do odd jobs around his neighborhood, like clean out garages, mow grass, pull weeds, plant flowers, clean windows, do small errands, etc. In other words, raise and earn the funds himself. Then you'll know how serious he is about aviation as a career.
But asking total strangers and/or friends to support of the costs of your kid's "dream" is disgusting. What are you teaching him? That you planned poorly and cannot afford to give him the training? That all he has to do to get what he wants is beg strangers for it? If you are really that ready to " we are willing to give up as much as we can", then have your husband get a second part-time job or you get one when the kids are in school, or on the weekends when your husband is home to watch them, or one you can work from home to help your son "find his wings". Your son is your responsibility, not the responsibility of friends or strangers.
I earned every dime it cost for my training, so did my Father before me and so did my son. If it takes longer that way, so be it. Nothing of value is free. And nothing of value that is not earned, is respected, admirable or appreciated.
If the Mother went on crowd sourcing to ask for help with medical bills for a child who has cancer or some other awful serious disease that they need help in paying for treatment of, that would be fine. But this nonsense is just that. Nonsense. You deserve what you earn, not what is given to you by strangers for nothing in exchange. What happened to parents teaching their children real life lessons? What happened to people being financially responsible in planning for how many children they ought to have that they can actually afford an education and/or training for to get them started in life with a career? Good grief.