Welcome to HCM,
You are Diabetes
type II for last 15 years, but your blood sugar level is not as it should be although you are taking many drugs really all types of oral hypoglycemic drugs.
When you take drugs for long time and disease tend to progress in so many years ,there is strong possibility of secondary failure and when blood glucose level is high even other drugs do not work properly .
Please see a good Physician/Endocrinologist
and discuss about starting Long acting insulin and many pre mixed insulins are there and some drugs like metformin
may be continued if there is metabolic syndrome
like central obesity and insulin resistance
even Zomelis and Glitazones can be used with insulin.
Once again diet and Exercise are still important even after 15 years.
If required B12 supplementation and other micro nutrients may be some what helpful.
You should have Glucometer and monitor pre lunch and pre dinner blood sugar with dose adjustments.
Diabetes can be controlled and PPBS must be