One way of doing this without having to program an import script is to generate those 15K variants in Excel and import them with the import function in the list view of the products variants (not the template). Make sure the URL says model="product.product" You will probably have to import them by batch of 1000 to avoid timeout. That would be 15 imports. A little time consuming but feasible. If you want to know how to format your excel document for the import, you can export a dummy record to see how it's structured and fill in that excel document with your 15K variants.

Thanks Fabrice. But I am more inclined with having no variants generated at all in the beginning and only generating a specific variant when a particular combination of attribute values are chosen by a visitor. Wonder if that makes sense. the reasoning is to keep the the system light and fast.