I've upgraded directly from 11.4 to 13.3 on various MX boxes so the version jump is fine. But not using HA clustering so there might be some nuances there.
You can use the dry run option to run ISSU upgrade without actually doing the upgrade and it will run a test for your config compatibility. Also check out the more detailed procedure with pre checks here.
http://www.juniper.net/techpubs/en_US/junos14.2/topics/task/installation/issu-upgrading.html