Good day I am looking for RAM for an iMac 5K, Late 2015. Will these fit or is there a better option? How can I filter sensibly on digitec according to Apple's criteria? At the moment 16GB (2x 8GB) are installed. Would you just add 2x 8GB or buy 4x 8GB new? I think I read that the RAM should ideally all be from the same manufacturer.