Conversely...
If the budget for a program gets doubled, it doesn't take long for all that money to find a place to go, usually things that a year later are considered "indispensable." This is a feature of government programs that goes far beyond PBS, and explains why our government spends four times what it did in the 1960s, in constant dollars.
As someone who's self-employed, I have had my income a lot more than 15 percent in the past. You know what? You work it out. So would PBS, (although I have a list of government spending I would cut, or at least freeze, first.) And hey it, wouldn't it be something to have them independent of government funding?