The bug numbers for the two performance issues are #6799 and #7535.  #6799 
is the most important of the two, and should be easy to backport.

http://krbdev.mit.edu/rt/Ticket/Display.html?id=6799
https://github.com/krb5/krb5/commit/5a28daefe46c1592936115a7b6c9c9b97957b14
8

http://krbdev.mit.edu/rt/Ticket/Display.html?id=7535
https://github.com/krb5/krb5/commit/090f561c631db7e4970b71cbe1426d636c39c77
a