You would be better off using the euro-keg as your MLT and reserving the regular Sanke for your BK. At 15.5 gal, I have had boil-overs in mine with 10 gal batches, so 13.5 would be really cutting it close in my opinion.
"I brew with a water cooler and some part from the toilet." - JohnnyO
"I do gravity feed the last gallon or two through my Therminator, but I expect you could suck start a Volkswagen before you could suck start one of these. - GilaMinumBeer
"..... Bull was right." - TXCurtis