If you mean when using the regular launcher you can do that by making folders for 1.8.9 and it will read the mods inside that folder, this feature only exists up to 1.12.2 though, 1.13.2+ it won't so you have to move mods in and out of folders but if your fine with keeping 1.15.2 in the 'mods' folder and 1.8.9 mods in a 1.8.9 folder then it should be fine.
Otherwise Third Party launchers like Twitch and MultiMC allow for separate version profiles to be created to work for each version.
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