I am currently doing some research on tires and rims (see my current post: Need new rims on '68.)
One of the resources that I am using is a Chevy High Performance article called "Get a Grip". The article lists tire sizes of 225/55 front and 265/60 rear as the max sizes for a 15" rim.
The 265/60 listed for the rear is 10.433" wide and your proposed 275 would be 10.827" wide which is a little wider than their recommendation.
The other problem that may arise is the overall height of the tire. In your other post, you gave a tire size of 275-50-15 which is 25.827" high. Using the max sizes from the article, the rears can be 27.52" high but the fronts can only be 24.74" high.
I am in no way an expert in tires and rims. In fact, I just figured out what tire sizes meant two weeks ago. On another note, I am putting a lot of weight on a magazine article that I can't verify as being 100% correct. The article also does not take into account any modifications made to the steering or suspension of your vehicle. Anyway, here's the links to the article referenced if you want to check it out: