Hi Julie, nice to hear from you again 🙂 Great that you are finding success with the LCHF diet and that it is largely bringing your levels under control. However, as you are discovering, you need less insulin as you are now consuming fewer carbs.
I would suggest going further than just trying to adjust your insulin - I would request a change to a different insulin regime. Adjusting a mixed insulin is not easy, as you will be reducing the slower-acting constituent at the same time as the faster-acting constituent that deals with the cartbs in your meals. Moving to a 'basal/bolus' regime, also known as MDI (Multiple Daily Injections) will give you much more flexibility with your food choices. This regime uses a slow-acting 'basal' insulin which deals with your background levels of glucose constantly being trickled out by your liver, and a fast-acting 'bolus' insulin which is used to cover the carbs in your meals.
Do NOT be afraid to approach your GP about this - it is your health, your choice, and your quality of life - if you believe you have found a diet which helps you maintain good control (and one which has many adherents!) then they need to accept this and help you with any problems that come along with it. The LCHF diet is not a 'fad' diet, but one that has been found to work extremely well for many people worldwide.
Unfortunately, we are not allowed to offer medical advice, so I can't tell you how you need to adjust your doses, only a healthcare professional who knows your full medical history can do that.
Looking back, I see that sometime ago you were suggesting that you might be Type 1.5 - did anything come of that?
Please don't be afraid to approach your GP or nurse. Different insulin regimes exist for the simple but important reason that there is no single regime that suits everyone, and your GP needs to consider your needs and not dictate them. Please book an appointment, and let us know how it goes, and good luck 🙂