Minecraft with mods hangs despite reasonably good pc?

My pc is already about 7-8 years old, but actually everything runs smoothly on it, except Minecraft.

So for example. Sims 3 with all 11 expansion packs and a Stuffpack + mods runs almost completely smoothly on my PC.

But as soon as I have even the smallest mod in Minecraft, my whole minecraft starts to hang and sometimes crashes completely or can't even open, which is funny because Sims is much bigger and more complex and has better graphics. The only mod I can easily use in Minecraft is optifine. And that is partly borderline. That's funny because I do not use texture packs.

That's why I wanted to know what that might mean.

(I know that Sims and Minecraft are two completely different things, but that's just an example of how my PC can withstand a lot.)

Without information about the hardware you can say nothing.