I don't understand what you are saying. You want to play Tekkit, but only Galacticraft? That's just one mod.
If you don't want 72 or 74 mods you can try to delete them from the mods folder inside Tekkit folder inside .technic
But I'm unsure if the game will crash on you if you do that, that's why I suggested you install the mod yourself on a clean minecraft
OR you can install optifine, which can help reduce lag.
You are really confusing me, when you're saying that you WANT to play tekkit, but with only 1 mod :confused: