How very distressing for you. I too had a fairly awful 3month period of suddenly being able to get below 15mmol after seven years of considering myself a reasonably well-controlled T2. You don't need to wait for your consultant appointment before (at least temporarily) changing your treatment plan. My care is shared between the GP and local hospital service, with most of the support services being offered by the hospital-based diabetic nurse clinic. I would suggest you ring your GP and ask if you can have a urgent referal to the nurse-led diabetic clinic to trial insulin while you wait for your consultant appointment. In my experience, they start you off on a very cautious dose, keep a close eye on you by phone, and order any additional blood tests you need. I ended up starting basal insulin last July with a question mark over whether I was T2 or T1.5, and did not see the consultant until Sept, by which time she had the results of the additional anti-body blood tests needed to confirm my T1.5 diagnosis.
This all assumes your local set-up is similar to mine. You say that you have been diagnosed as T1.5, in which case you are a big step ahead of where I was this time last year, you're also active on this forum, so a lot of positives, very best of luck with the next steps! xx