OK, so replacing a 15x6" 40mm offset wheel...correct?
So you add 3" to overall width. 1.5" to each side of the wheel centerline. The new 35mm offset moves the wheel hub mounting surface 5mm inward towards the strut, pushing the wheel assy 5mm outward away from the strut.
There are 25.4mm in an inch. You've added 1.5 inches width to the inner edge, and have only moved the wheel "outward"(away from your strut) 5mm(roughly 1/5 of an inch, guesstimation). You'll need roughly 1.25" extra room(quick guesstimate, not including a safe margin of strut clearance) to put the wheel on. THEN, squeeze a tire sidewall into the equation. You probably had less than 1.25" rear clearance with the factory wheel...but this all needs to be verified "in person".
As always, these type of questions are usually only answered with a test fit at a tire shop that has a wheel with similar dimensions to what you want.
Rays has +15, +22, and +28 offset 17x9 TE37...
http://rayswheels.co.jp/cgi-bi...=TE37
..waiting for Chet to punch some holes in the above theory...