I've got the suspicion the problem is caused by DirextX12 - another user told me Bungie switched from 11 to 12 and that's not supported for anything but Win10. There are reports from other games - most famous one might be World of Warcraft - with same or similiar problems. In the example of WoW they've worked out some kind of a fix for Win7 users. But that had some problems as well... in the end Directx12 did not reduce performance problems but caused them... Even if you're on WIn10 - if there is unsupported Hardware it wont work.