The two affected forums are Xbox360ISO.com and PSPISO.com. Details about the 2015 hack can be found on various places on the internet, but this Reddit discussion is definitely a good place to start, especially for possibly affected Xbox gamers.
According to Have I Been Pawned, “[i]n approximately September 2015, the XBOX 360 forum known as XBOX360 ISO was hacked and 1.2 million accounts were exposed. Along with email and IP addresses, the vBulletin forum also exposed salted MD5 password hashes.”
As both Xbox360ISO.com and PSPISO.com are pirate sites for the purpose of sharing illegal copies from console games, Microsoft itself is not affected.
But as those sites also have a thriving community that covers many tech-related topics, the leak will not only affect software pirates. If you ever registered at one of those sites, you now should definitely change your login-credentials as the leaked passwords might be on sale for cybercriminals. If you had used similar passwords on other sites, you should change your login data there as well.
On Troy Hunt's Have I Been Pwned you can check if your data is part of that leak. But anyways – even if it´s not, changing your password is a good idea. Partial leaks are not so uncommon.