If it's 15 gallons of beer, try the following:
Get a beer nut and hose barb. Hook the beer nut up to their sanke coupler with an "Out" Corny QD. Hook that to your keg. Then make 1 or 2 (Depending on how much beer is there) out to in hoses.
Hook it up:
Sanke > 1st keg "Out. 1st keg "IN" > second keg "Out". Second keg "In" > 3rd keg "Out". Open the relief valve on the last keg.
The beer will flow to the first keg until it's full, then flow through it's gas "In" port to the bottom of the next keg, and so on.
The nice part of all of this is that you just need to hook it up. When the sanke kicks, you'll have 1, 2, or 3 full kegs of beer and you didn't have to swap lines around or blow beer out a relief valve because the keg got full.