The reason the load times increase is because by default Factorio diffs the entire data.raw for every mod to determine prototype history, and these terraformers add approximately 200 or so megabytes to that total. So after this mod loads, every other mod has to diff a massive amount of data.
See https://forums.factorio.com/viewtopic.php?f=28&t=88218&p=507721 for more details
I got the loading time reduced in my personal modpack by moving data.lua to data-final-fixes.lua and adding an optional dependency (to control mod loading order) on every other mod in my modpack. Adding a z- to the beginning of the mod name as Rseding suggested won't work in larger mod packs since mods are first ordered by their dependencies before their names. What might be the best way to do this is depending on some hack like https://mods.factorio.com/mod/data_final_final_i_swear or similar. (This example adds optional dependencies for every mod uploaded to the mod portal, ensuring you'll be last. Although, you will need to ask that dev to be excluded or you'll have a circular dependency since this mod is already included in that list.
Or, if you don't care about prototype histories in tooltips, and more importantly having mod settings grouped by mod name, you can edit config.ini to disable prototype history. The game will load much much faster, but you lose the aforementioned features
