I've mostly brewed ales and now trying my hand at lagering a Kolsch (using Wyeast 2565 in this case). I understand for a 5 gallon batch of beer, primary for this yeast strain is typically done between 58F-70F for 1-2 weeks, then transferred to a secondary (carboy or in some cases, a corny) and lagered ~38F for 4 weeks or so, then force carbonated for 2-3 days (please feel free to correct me if this sounds crazy). However, I'm looking to brew a 15 gallon batch and I'm getting hung up on how to lager 15 gallon batches. The primary would be done in a conical at same temp range listed above. Once primary is complete, I don't want to keep the beer in the conical for 4 weeks, so what vessel would work best for the lagering stage in this case? Would transferring to a 1/2 bbl keg for lagering do the trick? Or should I worry about leaving a little more headspace? Any suggestions/recommendations? Thanks!