the 15% bump is a politcal phrase
that refers to the challenger's convention, which also used to be connected to the V.P. selection.
it's just a loose phrase, not a literal number. and it would apply to polling done in the days immediately following the convention.
there's a plethora of polls coming out right now, and frankly, they all look pretty good. both bush & cheney's negatives are real high (finally!), and there seems to be a real buzz for this ticket that's crossing demographics and regions.
also, national polls are just a buzz-joy snapshot anyway.
all that matters is the state-wide polls in each of the 15-20 swing states. that's what you want to be watching.
how's the match-up in Ohio, Michigan, Florida, Pennsylvania, Louisianna, Colorado, Arizona, New Mexico, Missouri, Illinois, Wisconsin, Oregon, Washington, Arkansas, Tennessee, Iowa?
how those individual states go determines the election.