HI and welcome to you and Titan!
Take a deep breathe.....your patience is not the problem. Your vet's LACK of patience IS! The normal starting dose for Lantus would generally be 1u or perhaps 1.5u twice daily (0.25u per kg. of ideal weight). We recommend making dose changes in increments of 0.25u at a time and absolutely not more than 0.5u. Our cats are small creatures and a 100% increase in dose is huge and will often lead to you skipping right past the best dose of insulin for your cat.
This is a marathon....not a sprint. Titan didn't become diabetic overnight so it's going to take some time to get him regulated and increasing the dose at the speed your vet is recommending is only going to slow the process down more. As strange as it sounds, too much insulin can look just like not enough because the cat's body fights against the insulin to keep his BG from falling to numbers he is no longer comfortable with or possibly numbers that are too low.
I think the dose needs to be reduced and then increased slowly and methodically in smaller increments to get Titan on a better path. Does Titan have any history of ketones or DKA?
We strongly recommend home testing because it lets you know when it is safe to give insulin and makes monitoring how a dose is working for him much easier for both you and Titan. Most cats get stressed out going to the vet and that alone can cause elevated BG which the vet then interprets to mean kitty needs more insulin.
The Science Diet M/D is NOT going to improve anything. It's high priced food no better and maybe not even as good as what you are feeding him now.
We can help you get on the right path with Titan so let us know if you'd like to learn how to home test and we'll help any way we can.

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