If you have the education requirements for the job you want, then do not acept second best by applying for use as a stepping stone. Even if not succesfull at OASC, you will have experienced the culture shock of the OASC process and be under no doubt where areas for improvement lay for a second attempt. More importantly; if you have done the homework necessary for OASC to meet expectations, you may well get the key to the career that you seek. You do have to be 17.5 years on entry for WSOp.
The danger is that you train to be a techie and said trade becomes a pinch trade that the RAF are undermanned. You then become a victim of your own success and find it difficult to leave because the system wants to retain you where you are.
The optimal answer to your situation has to be 'Go for gold' with the Techie route as a productive alternative. If I maybe blunt for a moment; 5xGCSE albeit good ones, is the baseline. Two years in sixth form and an A Level or two changes your options significantly. At 16 years, two years of further education can and probably does sound like a life sentence, but in the big scheme of things it could well be the best thing you ever did.