fpcupdeluxe is great if you want to get a particular revision or build cross-compiling.
If you need a stable version, just download the setup from. The docked IDE is the default option for this version.
2.5 MB is for most of the Lazarus Component Library (LCL) with minimal size increases even as program complexity grows. For example, Dadroit JSON Viewer EXE is less than 6 MB while having complicated tree views, JSON handling, networking, and more.
By the way, an empty CLI EXE on Windows is less than 50KB.