You are way to heavy for that bike. 15.5 Stone=217lbs. But....... if your wanting to just learn how ride, like learning to use a clutch and basic bike handling it will be OK. And just barely at that. Really you need something much larger in power to accommodate your weight. Otherwise you will be very disappointed with the bikes performance. How tall are you if I may ask. Im 5'6" and weigh 210 lbs. And I personally would feel like a circus clown riding an 85. Granted I have many years of riding experience. I ride a 250 two stroke. Way more power than I really need but I have never used all of it either. It may be worth your while to invest in a larger bike. Based on your weight even a 125 would be really to small but better than the 85. I would even consider a 250F (four stroke engine). Still a bit small in the power rating but the overall size of the bike will be better for you. And the power will be better. You could go with a 250 two stroke bike. Yes it has heaps more power and will likely scare you. But remember. Just because you have all that power doesnt mean you have to use all of it. Eventually you will get to a point where you will want more power or even need it. The 250F or 250 two stroke will provide that for you when your ready. Where the 85 will only leave you wanting.
Bare in mind this is only my opinion (my 2 pence worth). But Others will agree with me, purely because your a full size person, like me. Should you choose to get a larger bike I recommend sooner than later. It will benefit you better in the long run.