“This license is free to use and incurs 5% royalties when you monetize your game or other interactive off-the-shelf product and your gross revenues from that product exceed $3,000 per quarter.”
If you sell the VR app, for more than $3000 a quarter then you owe, 5%. If you are giving the VR app away (I wasn’t quite clear from your message) then there are no royalties. Basically, if you make money off of selling the product of your work in the engine, and that goes over that threshold, then you owe Epic. If you don’t make money from it, then you owe them nothing.
That’s my non-lawyer, laymen’s reading of the license. See the FAQ: