Seems kind of odd you would be on anything else for your sugars if you are on insulin. Did he indicate why he had you on insulin and a sulfonylurea? That's a recipe for hypoglycemia. Usually you adjust you units of insulin (basals and post-prandials) to control your sugars. The glipizide would stimulate further insulin release and probably make it harder to dial in your range control with insulin.
The guidelines say insulin is basically your last resort if other meds fail - usually docs have you go off all other meds and just use insulin. Before getting to that point, you're usually started on Metformin, then add another med if you can't gain control, and usually a 3rd med if it seems likely to be successful and avoid resorting to insulin.
Here's the link for current treatment guidelines from the American College of Endocrinology. I've seen all Family Med residents (so not just Endocrinologists) have the notecards of this algorithm in their pocket or on their desk. I promise, it's not dense at all. Page 6 has the meat of what I mentioned above:
https://www.aace.com/files/aace_algorithm.pdfIf you had a UA a few months ago, then your kidney function is probably not the issue. Your doc is probably on the right track with stopping the dual-therapy.