Hi, PJColbert, you're getting warm---er, and you're on the right track.... however, I don't know what model and year of iMac you have, you can find that by going to "About this Mac" under the large Apple icon, top left of your screen and it'll say something like "iMac XXXXX" and give you the year, basic specs about it, etc... that would be helpful to me (and US)...also there IS something you should know which is very important, at least for this question and this problem...the Mac OS, from Catalina onwards, breaks all 32-bit support for everything, and I do mean EVERYTHING, browsers, software, applications, plug-ins.... so, web browsers, software, applications, plug ins have to be 100% 64-bit and Catalina compliant in order to work properly and effectively and at full speed, with no buffering or stuffering or problems at all..... so, it's all 64-bit, Catalina compliant, or nothing....that's half of it, the other half is that you have barely enough, the bare minimum amount of RAM/memory to run the Mac OS....you said you have a late 2015 iMac, yes ??? If you follow this link, and this is for a Retina imac from Late 2015, you can have up to (the Max) RAM/memory of 64 GB.... https://eshop.macsales.com/shop/memory/iMac/Retina-5K2015/DDR3L
that's from a reputable and known good vendor/dealer of Mac memory/Ram and other mac accessories, parts, eg SSD's, hard drives, etc.... and your other 3 choices are: do you want to go for Max performance and size on that, which is $700 USD plus shipping and taxes, or would you prefer the value package of 64 GB which is $530 USD plus shipping and taxes.... 32 GB would run you $350 (16 GB x2) for max perfomance, 32 GB for the Value package would be $280 plus shipping and taxes.... you have 4 memory/ RAM slots in your iMac total, and I'm guessing you have 1 8 GB stick in there.... or 2 4GB sticks in there.... and that's it... OH, and here's the nice part...upgrading the RAM/memory in your iMac is very easy, and it's something you can do yourself, it's definitely user-upgradeable after you bought it, which means that installation of new/upgraded Memory/RAM is.....FREE !! as in, it costs you nothing, you don't have to take it in to get the memory/ram installed, you don't have to book an appointment with either an AASP (apple authorized service provider) or an Apple Store with Genius Bar... and you won't have to wait a long time to get it done, or to have it done for you (unless you want to, for both things) , if you were to buy the Memory/RAM sticks/modules, and they'd be shipped/delivered to your house, , and you'd received them....you have them all in your "hot little hands" , installation and upgrading the RAM/memory would take as long as....oh....20-30 minutes (maybe I'm overestimating the time here, but I do tend to take lots of coffee breaks) and boom !! done... Max ram/memory if you wanted it, or 1/2 the Max, or whatever, on your iMac.... 8 GB (Gigs) is just barely enough.....
how does That grab you??
John B