The purpose of your security clearance is to ensure you an individual trustworthy enough to entrust with information which, if released to others, could damage our national security. It is not designed to be part of the interview process. They don't care about your suitability for the job, only your reliability.
OCS is a crap shoot. OCS (not OIS) exists primarily to fill the needs (Bodies) of the officer community that other commissioning sources do not provide. Before applying to OCS you pick two (maybe three) designators, or communities (SWO, SWO-N, Aviator, Supply, etc.), you want to apply for. How many slots are available depends on what the needs of the Navy are (how many officers are needed) and how many bodies USNA/NROTC/NUPOC/NECP/ECP/etc. can provide. So it becomes a crapshoot based upon the economy (good times - officers leave in droves so there are many billets, bad times - nobody gets out so few billets), the Navy's situation (are we rightsizing, shifting the communities, etc.) and sheer luck of who comes out of other commissioning sources.
That being said there are always some billets. Some are there just so enlisted people with degrees can compete for officer programs, other are there because there are always some gaps. The other to remember about applying to OCS when you're enlisted is that you're competing with other enlisted folks -so they'll compare apples to apples. My point is that if you apply to OCS you're competing against other Fleet sailors who are all ready at sea, P.O. 1s, warfare qualified, EWS qualified, etc. You're not comepetitive, in general, until you get to the Fleet (which is two years after enlisting in the nuke program).
My final thought is - if you enlist with the sole purpose of being an officer, you'll experience a lot of heartache and frustration. The only option you have available with a degree is OCS. You'll see your classmates getting picked up for STA-21, USNA, etc. and you are shut out of OCS because you're not competetive yet
I DID get picked up OCS after 2 years at sea (qualified EWS, SS, etc.) but I wasn't always happy in NFAS and NPS when guys with lower GPAs were headed off to college and commissioning and I was stripping and waxing my barracks room.