The debug build feature for allocation statistics "AllocStats" (controlled by develop flag -XX:+PrintMallocStatistics) slows down the VM in fastdbg build even if the feature is not used (see JDK-8227597).
Note that NMT is available so "AllocStats" seems to be superfluous: e.g. "-XX:NativeMemoryTracking=summary -XX:+PrintNMTStatistics" can be used instead.