Can EE look at the specs for my current iMAC and tell me if the refurbished one I want to get from Amazon is a decent upgrade. Sometimes it's hard to tell except for processsor and RAM. Not sure the manufacture date on the refurb one compared to 2015 on my current iMAC.
Sorry, I more question. Is going from 8GB to 16GB give better performance if I stay with i3, or does going with i5 and sticking to 8GB give better performance?You really need to get 16 GB on Intel Macs for anything that uses Monterey (OS X 10.9) or newer if you plan on opening more than a few tabs at a time and not want your system to swap to disk, which slows the system down. Yes, SSDs are faster than HDs, but it's still slower than RAM.
After about 5 Years you can't upgrade to the current OSx version,https://support.apple.com/en-us/HT201624