Could diabetes type 1.5 be the underlying cause of tia like symptons, hypertension, hi glucose, low mpv, and low kidney function+protein in urine?

Yes : Type 1.5 diabetes involves autoimmune Insulin deficiency in addition to the Insulin resistance seen in type 2 diabetes. Cardiovascular problems, retinopathy, kidney failure, etc. Are sequelae to this disease. Tia risk is markedly increased by these factors.

Better control: While diabetes itself is unlikely to directly cause a TIA, it is an important risk factor for TIA and stroke. Better glucose level control will help prevent TIAs and strokes from happening.