First, it isn't the overall deal. It is the guaranteed money and money in the first three years that you judge a deal . $20 million in guarantees is top tier money.
Second, name one QB who is making $15 million a year. Manning's deal , which I am still the biggest among QBs, was for $14.17 a year which is not three times as much as Delhome who is averaging $8.5 million a year with his new deal. In fact that isn't even twice as much. And if Manning still has the best deal for a QB, no one else is making twice as much as Delhomme either.
Third, as far as I can telll the only QBs who are currently playing who are in the range you talk about are Manning, Roethlisberger ($12.75 mil per year), and Carson Palmer ($13.2 million). Even Brady is only making $10 million a year. Aaron Rodgers got what was considered a blockbuster deal last year at $10.8 mill per year with the same amount guaranteed as Delhomme. Tony Romo averages $9.6 million a year. McNabb makes $9.58 million per year. I think Matt Ryan is more, but it has been publicized that his deal is much less than advertised. So I am not sure what his average is although the inflated number puts him at $12 million. I still don't think you can find more than 4-5 QBs who average over $12 million even with bogus years included.
So I think you are way off on your numbers. I bet that if you look at the per year average and the guaranteed money, Delhomme probably ends up in the lower part of the top ten in compensation.