You may want to consider switching to a longer-lasting insulin. Blood sugar control can really improve when the insulin lasts longer. Both Lantus and Levemir are depot-style insulins, which means that some of each shot builds up in the body and slow releases, providing longer control and keeping the blood sugar flatter. Most kitties on larger doses end up on Levemir because it is ph neutral. Lantus is slightly acidic and can sting. Punkin got up to 15.5u and didn't seem to mind the Lantus at all, but some do notice it.
If there is any inflammation in your cat's mouth, it's probably a good idea to have the dental done. Inflammation or infection can raise blood sugar, and higher blood sugar means a larger insulin dose. We don't usually suggest people get their cat tested for a high dose condition until the get to about 6u.
The high dose forum (this group) is inactive and has been for some time. At the moment, there are many high dose cats in the Lantus/Levemir insulin support group.
Here is a link to a page on that group that has the most recent information on acromegaly, including how to get tested for acromegaly and insulin autoantibodies.
Most people have to go to work even with a diabetic cat. We got the Petsafe 5 compartment feeder and set it up to go off while we were gone to work. You can put high carb food in the feeder if you think you might need it.