What you will need to do is check on the shower head what they class as High/low pressure...ie Litres per minute.

Then spend about £4.99 on a water pressure tub

Basically it is a can with a gauge on the side, You turn on your tap and run it through the can, and on the side it will show a gauge and that will point to how many litre per minute passes through it......Therefore finding your water flow rate..

See what it is and there is your answer