change server size from 16g to 15g

testing/benchmark/system-profiles/15gb_v0.tfvars

@@ -0,0 +1,24 @@
+user_name = "USER"
+
+ess_region = "azure-westus2"
+deployment_template = "azure-cpu-optimized"
+stack_version = "8.16.0"
+
+# APM bench
+
+worker_instance_type = "c6i.2xlarge"
+worker_region = "us-west-2"
+
+# Elastic Cloud
+
+apm_server_size = "15g"
+apm_server_zone_count = 1
+apm_shards = 4
+
+elasticsearch_size = "120g"
+elasticsearch_zone_count = 2
+
+# Standalone
+
+standalone_apm_server_instance_size = "c6i.2xlarge"
+standalone_moxy_instance_size       = "c6i.4xlarge"