£145 dual is not a bad rate these days. For Microlights try Kevin's school based at Leicester. Otherwise try Sibson, Shacklewell Lodge, near Rutland Water or Spanhoe, near Corby.
Just remember "cheap" might mean "Cheep", cheep" as they boot the fledgling out of the nest...............!!!!!!!!!!!!!!
Though at 15 I do know where you are coming from. I was that age 65 years ago and could not afford it either.
Best of luck, it is worth the sacrifice.