As married people, unless they cheat or remarry I think there is a fair chance that sex as it is after 15 or 20 years with their partner is pretty much going to stay the same. So, excellent, good, bad or whatever, it will be what it is. This does not include of course single people, cheaters, or couples who partake of sex outside their main relationship with their partner's permission.
Do people just accept bad sex(is there such a thing??)? Does anyone communicate? You owe it to your partner to be all they need you to be in the bedroom, and beyond.