Ram Upgrade for Late 2015 iMac

I would like to upgrade from 8 to 32 gb of ram on my (late 2015) iMac as I work a lot with Lightroom, Photoshop and Affinity Designer. I have found that I can't have 2 or more applications open simultaneously as my mac freezes up. It's always been frustratingly slow even with one app open. A 10 minute job taking me a good 1-2 hours to complete! Also, since updating to Big Sur this problem seems to have gotten worse.

I have looked at what ram products I might need and found the following: RAM MUSHKIN IRAM MAR3S186DM8G28X2 16GB (2X8GB) SO-DIMM DDR3 PC3L-14900 2RX8 DUAL KIT FOR MAC

As I am not tech savvy to that extent could someone please tell me if this would be the correct product? Also, if anyone else has upgraded their Ram I would appreciate your feedback and experience on doing so. Is it worth upgrading to 32 (from 8) or do you think 16 would suffice?

Thanks so much for any input!! Much appreciated!

Lena