Real-Time Monitoring Tool (RTMT) shows a LowAvailableMemory alert, indicating that there is less than 10 percent free physical memory on the system (using the default threshold). This usually occurs for the publisher.
The warning is most likely cosmetic.
Through DLLHOST processes, Windows expands and utilizes the physical memory that is available for caching, especially Structured Query Language (SQL) and Internet Information Server (IIS). This can cause a low amount of available physical memory to be seen, especially in a publisher. These processes are intelligent about the amount of memory they use, and if the physical memory available gets very low (less than ~5MB), they release cache memory so other processes do not get swapped out to disk.