I don’t recall compilation being slow. The Clipper app for small businesses that my father created used overlays because it couldn’t fit in memory, yet compilation was still fast (all of this was happening on an XT). Linking, on the other hand, was painfully slow, but one could use Turbo Linker if overlays weren’t needed—TL was unbelievably fast. Later, Blinker came along. It was slower than TL but offered excellent support for overlays (and a bunch of other useful features) while still being much faster than MS Linker.