Hi Neil,
The minimum agent version supported by Windows 2012 R2 is 11.3 SP3, and not 11.3 SP4. Please refer to the agent compatibility matrix below:
https://docops.ca.com/ca-workload-automation-agent/11-3/en/release-information/system-requirements-and-supported-platforms/ca-workload-automation-agent-platform-support-matrix#CAWorkloadAutomationAgentPlatformSupportMatrix-Windows
The agent 11.3 SP3 is also supported by DSERIES 11.3 SP1. Please refer to DSERIES compatibility matrix below:
https://support.ca.com/phpdocs/0/7833/7833_WA_DE_Support_Matrix.pdf
So, based on above, you can use DSERIES 11.3 SP1 with an agent 11.3 SP3 installed in a windows 2012 R2 machine, with no problems.
In addition, we highly suggest you to upgrade your DSERIES server (and Desktop clients) at least to the top of 11.3 version (11.3 SP3). This can be done applying patches.
The patches are available for download at the following link:
https://www.ca.com/us/services-support/ca-support/ca-support-online/product-content/recommended-reading/technical-document-index/ca-workload-automation-solutions-patches.html?intcmp=searchresultclick&resultnum=2
If you have any doubts/concerns regarding DSERIES upgrade process, please open a case in CA support online. We will be glad to help you.