fast fill faucets and fast drain for 70 gallon walk-in tub
It's likely you can only reasonably change the draining. If you have 1/2" from the street then you're stuck with that. 1/2" can work great though your utility's pressure or what they push &amp; what you pull will be the limiting factor, so you're stuck there too.

However, you have a minimum of a 3" drain line for the toilet &amp; the tub can possibly be taken up to that for very much improved draining. I say possibly because the tub may only accommodate a 2" maximum drain or you have building structural members that can't afford 3" losses or a 3" pipe configuration can't actually fit under the floor...it's not just a right turn into a straight pipe.