I think you are going for the first thing that sounds like it will make you money. Plumbing was last year's goldmine - now we have been relieved of the shortage largely by quality Polish plumbers.
If you are clutching at straws on what to do post-school, take a good look at what inspires you and are good at, and go for that instead.
You also won't save £10k a year from a £15k per year salary once you have taxed it.
PS - don't use words like "gonna" on this site - write properly or you'll be massacred by the grammar police.