At the moment you think that £15 per hour is low wages for plumbing. But did you know that plenty of British Gas corgi qualified fitters are on £10 per hour? and also that many of us when we calculate the hours we do trying to run our own business are on less than minimum wage?
I remember sitting in a classroom listening to the lecturer saying how we (plumbers) are all on £40 an hour. He was saying it with a tongue in cheek mannor but I thought it was a double bluff. But now I realise he wasn't double bluffing he knew back then that what is reported in media and publicly perceived about plumbers wages is contrived.
As I am sick of repeating I earned more as a nurse. Print that in your newspapers and put that on your house makeover shows.
Wake up son, you are about to get a huge reality check.
As for working for family, I don't try to charge but if they offer money I accept it gracefully. In the same way some customers like to tip me, and I always accept it.
Similarly if I can help friends with fittings and stuff I do. A friend and I recently shared a solar project that is we bought in bulk and divied up. He then found he needed all sorts of plumbing bits and pieces I just sent him what he needed. He is out of business having had his ideas stolen by his supplier and not being able to afford to sue them, and nobody to do it for him. So I didn't expect money.
Friendship and family are special cases. You give to friends and family and if they feel led to give back receive it greatfully if they don't be cheerful you have done the right thing, it'll come back to you in some other way.
We also get this with vulnerable poor customers, you end up doing freebies for them. Bigger companies won't do that its one of the shames that sole proprietors are doing this essntial community service and that well known large companies don't. Perhaps they should.
At the end of the day it is how you conduct yourself in life not how much money you have made that you will be remembered by.