What is your current rim/tire combo? With this, add the dimension of your new proposal, break out the tape, and see where it falls by comparison. It sounds like you are adding one inch to both the inside and outside compared to the 15x8-4.5bs

Of course, you can run a 295 on an 8" rim, you just have to run it at a lower pressure.

295 is 11.6 inches. On a 10" rim, this only allows 3/4" of sidewall bulge on each side of the rim. A 9.5" width rim would be ideal.