Tips on increasing speed/usability?

My FIL had an iMac that was end of life, which is annoying for him as websites started loading incorrectly or not at all, Mac Mail was giving issues, etc. So I tried to revive it using OCLP. And it works again, but it's super sloooow. 15-20 minutes to start up. 10 minutes to start Mail or Safari. I think it's a memory issue as his backdrop image often fails to load, and only pops up after half an hour or so. I really think the thing is swapping like crazy.

Is there any way to tune MacOS as to use less memory? Or failing that; make it use a swap partition on disk? Or any other things that may increase performance?

Thanks!

submitted by /u/TheAfricaBug
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