Is this Vitamin B12 (Methylcobalamin) 1500mcg tablet safe for a diabetic patient whose B12 level is 147?

A B12 level of 147 is on the lower side, and it's actually quite common in people with diabetes, especially if you're on metformin, which can reduce B12 absorption over time. Supplementing at this dose is generally safe and often exactly what's needed in this situation. It's still worth having your doctor confirm the dose and how long to continue, based on your full lab picture.