Guess the answer depends on what you consider 'high visibility features', eh.
- master database replication?
- multi-path replication?
- improved db resync support? (more of a RS feature but requires some ASE interaction)
The list goes on and on ...
I'd either:
a - spend an hour (or two?) going through the RS 15.6 New Features and RS 15.7.1 SP200 New Features guides looking for any ASE-specific features you know you'll be using soon
or
b - [preferred] complete the RS upgrades to 15.7.1 (ie, don't worry about what's (not) supported by RS 12.6); and I'd highly recommend not actually upgrading your RS 12.6 instances but rather building out a brand new set of RS 15.7.1 instances so as to make sure you're not bringing along any unwanted garbage/corruption from the old RSSDs (every client I've helped with RS upgrades has had tons/years of garbage/corruption in their RSSDs ... it's always nice to start with a clean slate ... though this obviously requires a complete set of DDL for (re)building the new RS instances)