The first load screen after a mega pack install can take 15–30 minutes. Do not panic. The game is indexing every single new t-shirt and sofa.
However, a true Simmer knows that a mega pack is just the starting block. Download the pack. Play for a day. Then, go into your Mods folder and delete the "Cute" shoes you never wear and the broken hair that clips through jackets. sims 4 cc mega pack download
Use these sources for safer mega pack experiences: The first load screen after a mega pack