12'x15' area rugs are very large rugs intended for areas larger than 15'x20'. They are large enough to fully accommodate most of your furniture and accessories on top of and within the perimeter of the rug. However, keep in mind there is limited selection in design in the rug world of this size rug.
12'x15' area rugs comfortably accommodate tables with 12 chairs allowing enough room to keep the chairs on the rug when pulled back for sitting.
12'x15' rugs are seldom used for bedrooms unless the bedroom is of an exceptionally large size.