Affects Version/s: 1.15.2
Fix Version/s: None
Using a loot table, I made an exploration map for EndCity destination type.
When looting from this table, the game completely freezes up for about 20s (counted) and then the map is generated and given.
This was for an EndCity literally 37 blocks away, found using the /locate command (which took almost no time).
My assumption is that this happens due to trying to do the "river" style on the map, and probably also affects Nether Fortresses in the same way (I haven't tested, just a guess).
Since this is the case, my proposal would be to simply make the "river" generation an optional value (like skip_existing_chunks) so that datapack authors can turn off this since it is unnecessary for EndCity. Or just make a check for dimension the structure is in and just don't do the "river" styling for end and nether. Whichever one makes more sense.
Here is the loot table I made for the endcity map: