XA transactions much slower on 14.2 than on 13.5

My boss asked me to upgrade one of the development  databases from 13.5 --> 14.2. One thing that we've noticed right away is that XA transactions (2-phase commit) are much slower on 14.2 than on 13.5. Were there any significant changes to the XA protocol in the version 14? Did anybody else encountered this problem?

When I say "XA transactions are much slower", I mean that commit and/or rollback take much longer. The SQL execution takes the same and the plans are identical to the 13.5 version. The application code is the same, using IBM WebSphere 9.0.4.
Regards

-- 
Mladen Gogala
Database Consultant
Tel: (347) 321-1217
https://dbwhisperer.wordpress.com