Hi,
The problem is indeed the amount of variants you have in your products.
For example on this page:
morenadancewear.com.au/shoes-for-her/sal...uct/178-160936-.html
The heel dropdown has 7 choices. The size dropdown has 15 choices. The sole dropdown has 2 choices.
That's 7*15*2= 210 variants data loaded on the page.
It's as if you're displaying a listing of 210 products, and if you do that, you'll see that it's about the same slow speed.
The variants system allows you to configure different images, description, price, quantity, etc for each variant of a product. That's why it takes so much resources.
In your case, no information changes on the page regardless of what is selected in the dropdowns. So you actually don't need variants. Instead of characteristics, you could create custom fields of the table "item" via the menu Display>Custom fields.
You'll get the same look, and the pages would display fast since no variants would need to be loaded.