Most likely it is too big - a 140/90-15 just barely fits without rubbing the swing arm brace at the front of the tire.

It IS possible, BUT, it is NOT a simple swap. The bolts for the siderails have to be swaped, AND the clearnce to the front of the swingarm is a issue, like versi said. I had one on mine for awhile, BUT, I have both Kaw pulleys on mine that move the axle back about 7mm. And the clearnce to the belt is VERY TIGHT.
So if you are just wanting to look at the whitewall, like a Shinko 777, do you REALLY want to go thru changing the pulleys, or maching the swingarm?
( I think egore is running a 150/90 15 whithout changing the pulleys, but it wouldn't work for me. Maybe it's the altitude up in Colorado, but not here in flat Fla..

i bought this 20 year old bike whit the original tyres!
There was a lot of miles to go befor one hit the cord
In anyway I put it in to my local  bike workshop, to get new tyres, new tubes, and ofcourse new oil and filter!
I got Bridgstone tyres, on the back I got 150/80. its still a lot of space to the swingarm!

What can i reply.. I can only reply as a formar biker.. 20 years a go, new Suzuki Savage LS 650 2000  made.. its a crap, I and my bike is old, but I stick up on it about this a bit becuse Im older then my bike!
In anyway my 2000 LS 650 Savage is  not  a crap.. but its almoste like having a new partner, telling that one love them in any case this dont make up for practical mantaince..its crappity smacking moste of it!