And you can just tell I'm a nerd because of this video:
tl;dw: Basically the greater the mass is of ice, the longer it takes to melt, because the ice within the ice is still cold. It was mentioned in one part of the video that an ice mountain that was formed in Boston from all the snow-shoveling took until June or July to completely melt. Heck, back in the day, they shipped ice from the Great Lakes to India by boat, even though a bunch of it melted it was still worth it to do so!