If you used Adaptive Server 15.5 features that are not available in the Adaptive Server version to which you are downgrading, additional steps may be necessary before downgrading your server. In addition, some actions must be performed immediately after downgrading.
Java in Adaptive Server – If user classes compiled by a Java version above 1.2 are installed, these classes do not work in pre-15.0.3 Adaptive Server versions. Earlier versions of Adaptive Server ignore the enable pci parameter. You can remove it. sybpcidb is not used by pre-15.0.3 Adaptive Server versions. This can be dropped if desired.
SQL Replication – See Upgrading Servers with Replicated Databases,
sp_addserver with <filter> parameter – If you used sp_addserver to create server entries with the filter parameter specified, you may have entries in sysservers.srvnetname column which are longer than 32 bytes. You must delete these entries before downgrade and add them back after downgrade.
In general, no additional steps are required when you are returning to an Adaptive Server version in which the feature was already available.