Officers will join on a 12 year Initial Commission. Ratings I believe generally sign on for 22 years or until they are 40. Both have the option to leave during phase 1 training or after completing their return of service (which varies by specialisation but is generally 3 years). An important thing to note is that return of service is calculated from the point at which you join the 'trained strength' (i.e. you've completed training and are joining a ship or boat as a member of the ship's company), which will be longer for officers (again, how long varies, I believe ME SM is one of the longest at something like 3 years). On the other hand, that's all valuable training, and the pay is significantly better! I don't think the return of service is any longer for those with sponsorship, but if you choose to quit before joining/during training or are thrown out for some misdemeanor or other you will have to return either all or part of the sponsorship money.
Anyway, to the original question - yes, if you're well qualified to be an officer they probably will ask you why you're not applying that route. That doesn't mean they're trying to change your mind, just making sure that your making your decision for a good reason and know the difference between the two roles. I wouldn't advise saying that you're reluctant to lead, as ratings are expected to lead as they progress through their careers, though not in the same way as officers are.
If you've got any other questions feel free to PM me, I know a bit about Naval careers.