Slow/Lagging whenever I play a game (on Mac OS X)

Hi! So I'm fairly inexperienced with emulation, and I've tried playing games such as Pokemon (both NDS and GBA games) using OpenEmu, or just downloading the ROMs and compressing/extracting the files, but either way my gameplay experience is just extremely laggy and I have to keep pausing the emulation just so it can "catch up" and not be slow just for a few seconds. I've been told to try toggling the emulation settings when playing with extracted files, but that just made things worse. Is there any way at all I can fix this, or is it simply because I'm emulating on a Mac?

Thank you! And I'm sorry if this had been asked before.