Hi,
The variants system is a heavy system. If you have too much variants so it will take very long time to load.
It require many requests, etc. So a better solution, is to use more categories in order to reduce the number of variants.
For example having the category "size of paper" will allow to considerably reduce the number of variants.
Regarding the quantity, Why are you using it as variant ? It's better to use the default quantity field.
With only these few things, the page load will be really faster than before.