I am not able to launch the virtual device, i am getting the following error, kindly help me out to resolve the mentined error]

C:\Users\polo\AppData\Local\Android\sdk\tools\emulator.exe -netdelay none -netspeed full -avd Nexus_5_API_21_x86
emulator: device fd:460
HAXM is not working and emulator runs in emulation mode
emulator: The memory needed by this AVD exceeds the max specified in your HAXM configuration.
emulator: AVD RAM size = 1536 MB
emulator: HAXM max RAM size = 512 MB
emulator: You might want to adjust your AVD RAM size and/or HAXM configuration to run in fast virt mode.
Cannot set up guest memory 'pc.ram': Invalid argument

thank you