…No, unions won’t help. In fact, it might make it worse. Unions will also take longer to load in than individual parts. Loading times will be worse with more unions.
I recommend you use meshes instead. Try learning blender, or turning your unions into meshes.
Here are some useful posts to help out your situation.
Forum Post 1
Forum Post 2
Forum Post 3
I am most definitely not an expert at this field, but I know for sure that unions probably aren’t the best solution. Go read the posts above. In fact, I’m going to go read them right now because it’ll probably be useful in the future.
Good luck.