Was listening to Minnesota Public Radio not long ago and I bet there were 15 to 20 between the NPR, State Network and Local inserts.
15 to 20 minutes? Sorry, you're hallucinating on that one, dude. ;D
I don't recall the exact "clock" for Morning Edition off the top of my head, but I know the "standard" clock (that Tell Me More, On Point, Talk of the Nation, and most of the non-newsmagazine shows use) goes as follows:
00:00-01:00 Billboard
01:00-04:00 NPR Newscast 1
04:00-06:30 NPR Newscast 2 (cutaway for local newscast)
06:30-19:00 A Segment
19:00-20:00 Local Break
20:00-38:30 B Segment
38:30-40:00 Local Break
40:00-59:00 C Segment
59:00-59:59 (nothing; legal ID local break)
That's an absolute maximum of six minutes of underwriting spots. More realistically it's three minutes and thirty seconds of spots per hour, since no station I know of fills the NPR Newscast 2 segment solely with spots (they do 2 minutes local news and then maybe a 30 seconds of spots) and figure 15 to 30 seconds of the legal ID break has to be the legal ID itself; a lot of NPR stations are actually networks, but of course this varies a lot.
And that assumes that 3:30 is solely given over to underwriting spots, which would be fairly rare. Usually at least 30 to 60 seconds are promos, and there's often a weather forecast or two in there somewhere, too.
Like I said, Morning Edition is on a different clock, with a couple more breaks, more newscast cutaways, and in theory I think you could somehow do about 10 minutes of spots but nobody would do that. At least five minutes of that 10 is for local newscasts.
Another thing you're not supposed to see...but if FredLeonard's observations are accurate (something I have to question given your not-terribly accurate screed there, Fred) then at least one station is seriously breaking the rules of their NPR Member Station Agreement...is news stories that are thinly disguised commercials for a product. You hear that a lot on commercial news stations, where a "commercial" is aired as part of a newscast and sounds like it's still part of the newscast, even though it's really a commercial. That's a major no-no on NPR member stations.