Warning! 2 cents of design opinion coming up...
From a design standpoint, I’m not crazy about mixing a rough texture of epoxy with shiny-smooth tiles with factory rounded edges.
You certainly can leave out 10% of the ‘colored sand’, but working the stuff into 1/16” joints is going to be something of a chore. And I also would forewarn you that you might not like not being able to feather and taper the edge of the epoxy like you can with unsanded grout. So, you might not like the somewhat uneven grout as it interfaces to the factory rounded edges.
If you really, really want epoxy, it would be worth making a mock up and grouting it before committing to the whole shower. Just an idea.
