My personal slot on walleye is 14″ to 18″ where legal to keep them in that range. Smaller ones don’t have a lot of meat on them, and releasing small ‘eyes gives them a chance to reach sexual maturity where natural reproduction matters. I also release walleye larger than 18″, as they are the mature females on whom spawning success depends in waters with decent natural reproduction.
Even in SE Iowa, where walleye populations depend on stocking, I release fish over 18″. They don’t taste as good, and have the chance to become real trophies. On the Mississippi down here, where the walleye population is self-sustaining, there is a state-enforced 19″-27″ slot on Illinois-Iowa boundary waters in addition to the 15″ minimum. I am all for those regulations.
I ate my share of 20″-ish walleye when I was younger, but unless the fish is likely to die if released, and it is legal to keep that fish, I will eat no more in that size range. My last such fish was a 22″ pre-spawn walleye I caught below the spillway in Winona about ten years ago. I was already releasing more of those fish, but I was a hungry undergrad, so I kept that one, which was perfectly legal. When I fileted her the sight of all those eggs spread out on newspaper was enough for me to stop keeping adult females. It was a “final straw” sort of thing, not an epiphany.