I had a lot of trouble with this, and the tutorial page on the MineColonies site isn't exactly helpful. Not sure if these are the best/most up to date versions of the files, but they are compatible with each other.
You Will Need: - minecolonies 0.13.74 jar file (from curseforge or another host)
-structurize 0.13.27 jar file (on curseforge as well)
How to Install: 1. download the above files
2. forge should install itself automatically, don't worry about any of the settings
3. go to your minecraft mods folder (%appdata% -> .minecraft -> mods)
4. put minecolonies and structurize into this folder
5. launch the forge 1.15.2 Install in your minecraft launcher
-the recommended version of forge for 1.15.2 does not work, 31.2.33 is the latest as of posting
-if you can't find your mods folder, you may need to launch the forge install once beforehand
Tips For MineColonies: I would recommend having the basics together before you start your colony (wood farm, good stack of cobble, some iron, etc.). Collect some wheat seeds, sugarcane, leather, string. Find a good gravel quarry.
You will need A LOT of flat space. The default colony is 8 chunks in every direction from the town hall.
Always make sure you can see the bottom of a build, or else you may end up buildings things in pits.
-JEI is a useful companion mod as the crafting recipes are hard to find online