I've had it for 14 years, I'm 31 now. It's always been a high-pitched hiss loud enough to hear everywhere if I listen for it. It took me about a year I think to habituate. After that it didn't really bother me ever. I've played in my band for ten years, touring, going to cinemas and clubs, listening to music. I think I've had a pretty good sense about when to use earplugs though, and I always have them with me. It never got worse for me and I only had smaller spikes that went away after a night's sleep. I define my spikes as when the sound changes. My baseline can go up and down in volume too, but I know that this is a matter of perception and not actual volume. Sometimes, when drunk for ex, the hiss can get ridiculously loud and I always marvel at how I just don't care emotionally about it. It's quite amazing how your brain can adapt and accept things. I always hated reading online about people telling me that habituation works when I first got T. But believe me, it does work, better than you can even imagen. It's like magic.
This changed about 3 months ago though after an accident with my stereo suddenly blasting on full volume. This spike is still going on and I'm a bit worried it won't go away. It's been changing and seemingly getting a bit better though, so hopefully it'll subside totally. It's sounds like one of my old spikes, which is a bit comforting. If my brain could heal it so many times before, hopefully it can this time as well.
But to answer your question; it's different for everyone ofc, but I had it loud enough to always hear it, and I'd say it affected my quality of life by about 5% (before this spike). In short, not a big deal!