I wouldn't think you'd have to change the specs if it's working on 11.5. We have several modules (of which NCM is one of them) and actually noticed a decrease in CPU on the main poller following the upgrade.
Use the following resources for planning and upgrading:
Use the Product Upgrade Advisor to build your upgrade path. The path provides the exact products and versions to upgrade in a sequence to the latest versions.
As you are upgrading NPM and other modules, use the multiple products upgrade guide.
The guide includes checklists and instructions to help you plan and execute your upgrade including the HW and software requirements to your multi-module environment.
When you are ready, download the upgrade package from the SolarWinds Customer Portal.