The Foglight Agent Manager (FglAM) is not releasing memory, the memory consumption increases by 10 - 15 MB per week.
Is that a normal behavior? Or is it a memory leak?
It is not a memory leak. It is the normal behavior of the JVM.
Per default the memory usage of the FglAM is limited by 256 MB or 1/5 of the installed memory. The limit can be modified by adding a vmparameter into the vm.config file. See solution SOL62217
Java is allocating as much memory as its needs, until it reach the limit. If a garbage collection happen and memory can be freed, Java is not always doing it, because memory which has been used once, might be needed in the future too. But Java will not cross the limit which is set. So if the limit of 256 MB is not exceeded and the FglAM is running without any problems, there is nothing to be concerned about.