Total tenure on H1B.... fresh + extension

My H1B petition has got approved, however the validity they have granted is only 1.5 years though it was applied for the full 3 year term.
My question is, can I serve the full 6 years term on H1B(fresh + extension)? Or the max I can get is only 1.5 years now and 3 years extension, i.e. 4.5 years?

It depends on the discretion of the VO. Based on the documentation that you are going to provide now, they may give Visa again for 3 years or based on the documentation that you are providing to them.