If you have trouble maintaining weight on 3000 cals at 150 pounds then it is probably due to a high degree of insulin insensitivity already, if not type 2 diabetes.
The main problems that diabetes doctors "have" with fat is that a) they believe it makes you gain fat and become less insulin sensitive and b) they believe that saturated fat is atherogenic and c) to a lesser degree they believe that eating fat reduces your insulin sensitivity for that meal.
a) does not have to be true. You do not need to gain fat eating more fat, but they just assume that the more fat the average American eats, the more calories and fat they are accumulating. Also more bodyfat DOES push you closer to diabetes. (If you have trouble gaining weight on 3000 cals you likely have hit the beginning of type 2 diabetes anyway).
b) The sum of research does not show dietary saturated fat as atherogenic. When the effects of high carbs that people who eat high saturated fat usually eat are remove, the higher saturated fat diet is probably anti-atherogenic.
c) It does reduce insulin sensitivity during a given meal, if you take x carbs and y fat and add 50% fat your acute sensitivity does go down, but if you replace carbs with fat and keep cals the same your insulin demands are LESS and your insulin sensitivity long term also stay higher which can keep you from going to the final stage of type 2 which is a dead pancreas.
Going below 100 grams of carbs a day has been shown to possibly raise blood sugar, and the lower you go the more erratic it can become because it upramps gluconeogenesis to provide glucose for the brain. You become LESS insulin sensitive at under 100 grams. Also stress hormone induced blood sugar spikes tend to be greater on a very low carb diet than on a 100 gram carb diet because on the 100 gram carb diet your not relying on a constant basal glucagon release to maintain brain glucose, and again that tends to lower insulin sensitivity.
In my honest opinion, a prediabetic will have the best chance at reversal if they get 100-150 grams of carbs then if they go under 100 grams because their body becomes insulin insensitive to preserve glucose for the brain at under about 100 grams a day.
Also, a low animal fat diet can further reduce insulin sensitivity by creating a choline deficiency.
Omega 6s (linoleic acid) has to be removed. Also, among MUFAs, Canola, even with low erucic acid lowers lifespan in rats.
Omega 6s cause inflammation chronically which reduces insulin sensitivity CHRONICALLY and elevates blood sugar chronically.
You can follow your doctor's advice and your consolation will be an apology 20 years from now.