I agree with
@Robin, that there isn't any clear definition and the medical profession use the term in different ways, which just adds to the confusion. I think using the term Type 1.5 makes it even more confusing because sometimes this is tied to LADA and seen as the same thing and sometimes it is used to refer to Type 1 diabetics who also have significant insulin resistance.
I think the term insulin resistance is also confusing. It is easy for us all to think we have a bit of insulin resistance when in fact we are just needing more insulin to deal with liver output..... So for instance, on a morning I need more insulin to deal with FOTF and that insulin takes a long time to work because it has to overcome that flow of glucose. If we were not diabetic, our body would be producing insulin to deal with that liver dump and we would be none the wiser about what we needed and when. This is not insulin resistance in my opinion although I have referred to it as insulin resistance before.
To me the way to tell insulin resistance is if we are needing substantial amounts of insulin (large doses) not how long it takes to work. My gut feeling is that if your carb ratio is 1:10 or greater, then you are not insulin resistant. As a LADA where your body is still producing some insulin this may slowly reduce over time and could easily lead someone to think they might be developing insulin resistance, but I have a feeling that 1:10 is probably about the norm, but exercise and illness will impact this of course.
I know a lot of people talk about a low carb diet causing insulin resistance but to me again I feel this is misunderstood and it may just be that the slow release of glucose from fat and protein makes it look like insulin needs are increasing hence IP developing but I think the liver may store and release more, as a result of this diet, particularly if not enough exercise is done. I do not see this as insulin resistance. To me IR is the reluctance of the cells to accept glucose from the blood stream and if your ratio remains more or less the same for meals then it isn't IR because post meal is the time when IR will be more obvious and much larger doses will be needed to cope with a normal amount of carbs.
The time it takes insulin to work is just a factor of our metabolism and not not related to IR but again I think it is easy to believe it is. As you now I use Fiasp and I need 45 mins most mornings prebolus before I eat. This seems really excessive and I have done a lot of thinking about it, but the fact of the matter is that it is working quite quickly because my BG levels stop rising after I inject it, but it is dealing with a strong tide of glucose from the liver so it looks like it isn't doing anything when in fact it may be working quite hard but I am just not seeing that reflected in my levels.
I still work on a 1:10 ratio but in the morning I often need an extra 1.5-2 units of bolus insulin to deal with FOTF. I don't see this as a ratio change because I need those extra units whether I have breakfast (and a bolus) or not, so I see it as a very separate factor and is actually a top up to my basal insulin at that point in the morning when the evening dose (if I took one) is tailing off and my morning dose hasn't kicked in yet but my liver is churning out glucose as it does on a morning. Those units don't have a bearing on what I eat.
What I do find is that I need more or less basal insulin depending upon exercise, my weight and illness. If I don't do enough exercise I need more Levemir, if I get fatter, I need a bit more Levemir and if I am ill, I need more Levemir. Exercise seems to make the biggest difference for me and is why I love Levemir so much. Again I don't see this as IR when I need more because I am not exercising, it is just that my muscles are not sucking it out of my blood stream more readily. If I need more insulin because I am ill, this is because my liver is chucking out extra glucose to help me fight the infection rather than that my cells are not responding to it which to me is IR.
Not sure how much of what I have written makes sense but I think there is a lot of misunderstanding about IR because we can't see it or measure it or know what is truly IR and what is just a ramp up of glucose release from our liver for a variety of reasons.
My guess is that you are not insulin resistant at all, but are misinterpreting liver dump and perhaps sluggish bolus insulin for IR when it isn't. I would be surprised if you are needing large doses of insulin which would indicate IR.