2000 Tacoma SR5, presently running 16"x10" Centerline "Cooler" wheels (discontinued now) which have a 4.5" backspace, If I go to 15"x10", will 3.6" - 3.75" backspacing clear using 12.5" wide tires?

 

clear the calipers?

 

like said, if yo have 16" wheels now, you most likely won't be able to fit 15s because of caliper clearance. Most Tacomas have larger brakes than the older trucks. you'll have to do some searching to figure out the wheel specs for the specific tire size you're wanting to install.