So I've just done this!!
Graduated couch to 5k I started at 121kg (126kg back in November when I was hospitalised for gallstones) today I'm 111kg.
For anyone thinking they can't do it you can! There will be times when you think you can't but that's you stopping yourself.
There maybe times when your body can't but it can be pushed more even through pain.
Keep going it's possible!!