Hi Carameline, I didn't get a blood glucose reading when I was first diagnosed in late October last year, but it would have been around 13-14 ish, so not too different from yours. My cholesterol was 6.4, so also similar.
I went on a 800 calorie a day diet for three months, sort of based on the
Newcastle diet which helped me lose 16kg. I did BG tests at home from December, and they were around 6mmol/mol fasting (normal for non diabetics is between 4 and 7).
When I got my bloods checked again in February, my HbA1c (which is a measure of the last three months blood glucose) had dropped from 80 mmol/mol in October to 42 mmol/mol, my fasting BG was about 5.5, and my cholesterol was 4.6. So it was about 4 months to get them both down.
I can't recommend throwing yourself straight into a very low calorie diet like I did, with hindsight, I'd probably do 1700 or 1500 calories for a month and then do the 800 calories, to give my body a chance to adjust to the lower level of food and reduce the glucose level a bit slower.
Your HbA1c is high, but there's others on the forum who had similar and got theirs down after some months, so take heart that it's doable. You don't have to do everything at once, take stock of what you eat currently, and think about how you can improve that.
If you change your diet to reduce your carbs, do it slowly, so your body can adapt to the lower levels. You may get blurry vision as your BG falls, as the eyes adapt to the new levels. It usually sorts itself within a month or two. Also, you're going onto metformin tablets and they may upset your tummy. If so, let your doctor know so that they can prescribe the slow release version.
Sarah