my punkin is on 8u - there are conditions that can cause them to need more than the usual amount of insulin. Insulin needs can be high if they have an infection that's unresolved (dental problems seem to often be part of that), are in pain, if they got to that dose by too big of increases in their doses, or if they have a couple of medical conditions, acromegaly or insulin resistance. and then, some kitties just need more. You can also have insulin that's not effective if it wasn't taken care of. It's kind of a one step at a time process to figure out if Buggy is getting a good dose or needs a change.
We have several people on here who can comment on doses - they will want enough information. Most of them are either in the eastern or central time zone, so you'll have more eyes on your question tomorrow.
in the meantime, they'll want to know if you have any data on how the dose changes were made - like how long you stayed at a dose, what the numbers were, and how big of an increase the vet had you make. If you can post any of that data - dates, dosages, blood glucose numbers (it helps to know how many hours after the insulin was injected that the blood sugar number is from), all of that data will help them.
most vets don't have a lot of experience with feline diabetes and a lot of vets don't seem to really understand lantus and how it works - people often get here after having made 1unit increases in their cats dosages. Here we increase by .25 units and stay put at a dose for several days. Cats numbers tend to get all wonky when the dose changes, even by tiny amounts, and we let them settle before making more decisions on the dosage.
You'll want to get a spreadsheet going - the instructions for doing that are under "lantus/levemir new to the group - read here"
http://www.felinediabetes.com/FDMB/viewtopic.php?f=9&t=18139 that's full of great information for you to start with.
i've probably overloaded you so will stop. you're in the right spot. we all help each other and we follow a proven protocol for helping cats become as healthy as possible with their diabetes. the folks here do feline diabetes 24/7 and really understand it. i know i've felt so lucky to found this site, and i suspect most of us feel that way.
glad to have you here. jump in. ask questions and we'll all do our best to help you & Buggy get him as healthy as possible.