Upgrading RAM Late-2015 5k iMac, Can I Combine RAM or do I need to Swap All?

[imdog]

Hey, so I want to upgrade the RAM on my late-2015 5k iMac, I currently have 8GB and think I want 32GB. Or is that overkill and should I just go with 16GB? I use this computer for music production in Logic with Native Instruments libraries, Izotope, Antares, Slate, etc. I do 4K video editing in Final Cut Pro. I bought the M1 Mac mini a couple weeks ago but returned it due to lots of bluetooth & display issues, so I'm using this iMac until a Apple Silicon iMac or Mac Pro mini come out with less issues.

So first off should I go with 16, 32, 64, or how many?
Secondly, what is the best configuration for that and should I combine the RAM with my old RAM or should I swap it for all new RAM? A friend told me that combining RAM that was made at different dates can lead to problems and it's better to swap for all new RAM? I currently have 2 4GB sticks installed (the ones that came with the iMac)


Thanks

 

[wilberforce]

Hey, so I want to upgrade the RAM on my late-2015 5k iMac, I currently have 8GB and think I want 32GB. Or is that overkill and should I just go with 16GB? I use this computer for music production in Logic with Native Instruments libraries, Izotope, Antares, Slate, etc. I do 4K video editing in Final Cut Pro. I bought the M1 Mac mini a couple weeks ago but returned it due to lots of bluetooth & display issues, so I'm using this iMac until a Apple Silicon iMac or Mac Pro mini come out with less issues.

So first off should I go with 16, 32, 64, or how many?
Secondly, what is the best configuration for that and should I combine the RAM with my old RAM or should I swap it for all new RAM? A friend told me that combining RAM that was made at different dates can lead to problems and it's better to swap for all new RAM? I currently have 2 4GB sticks installed (the ones that came with the iMac)


Thanks

I had a 2014 iMac, and I believe 2015 iMac is the same.
I used 2x4GB Apple RAM plus 2X8GB Crucial RAM for a total of 24GB, worked great, no problems.
You can combine different size RAM sticks, provided they are in pairs so that each channel has the same amount of GB.
This means install them in order ABAB, not AABB. Just make sure they have the same spec (like MHz frequency)

btw, this is not true for the 2020 iMac, where all 4 sticks should be identical otherwise performance is degraded, but that is a special case.