first of all 15x10 is very wide. but im sure it can be done.
6" BS will never clear the strut. you want the BS to be no more than 4.5 - any larger of a number and the tire will touch the strut. most R50 owners get the best results with 3.75 to 4 inches of backspacing..... the smaller the number, the more they will stick out. of course this is affected by width too
my stock rims were 7" wide with a 4.5 BS
my second rims were 8" wide with a 4.5 BS so the rim was actually in the same spot on the inside but stuck out an inch farther on the outside
my newest rims are 9" wide with a 4.5 BS..... so they STILL the same orientation (if you ignore rim diameter) on the inside but stick out 2" farther than stock, on the outside
basically, on this SUV, stick to BS between 3.5 and 4.5 (with those being the two extremes) you should be fine.