It's getting noticeable after 15-20 minutes of playing
Easily fixed! Just disassemble the headset, remove the battery, display, speakers, circuit boards and lenses. Reassemble and enjoy your lightweight device.
Dan larsen commented
As was mentioned, this isn’t something that is going to be resolved in software. The best fix for this is to use a counterweight battery. It removes much of the weight on the face.
Greg Madison @ Unity commented
Not something that will be resolved with a firmware update! ¯\_(ツ)_/¯