For that amount you can bet that the company will request comprehensive medical information.
If you applied today and were declined, there is nothing to say it will effect your application in a couple of months or years down the road. People who recover from Cancer can be declined at differant stages but be accepted at others.
Applying now and getting a decline means that there will be red flags on your future applications (by that I mean simply notes stating that you were declined and the reasons why).
Not applying now will still mean medical information will be requested and they will probobley find out that at some stage you had a high BMI (when they request information off your doctor).
I have seen people being declined in one Assurance company only to be accepted in another, it does happen, differant companies will take on differant clients.
Really what I am trying to say is that I dont personally think it makes that much of a differance (if any) if you are declined now or wait until you think you have a better chance of getting it.
Another thing to note is that in certain circumstances you may be accepted with a loading or a rating (penalty fee on premium). The Assurance company may offer to waive this penalty down the road if your health improves (*This would be clarified during application stage), which means in your case if the loading was because of your BMI, they would consider reducing or taking away your loading if you got that down.