Troubleshooting: poor flow from gravity fed shower

[DeeEyeAye]

I've installed a thermostatic shower which is plumbed in from the header tank and hot water cylinder. Head on this system is about 3m from the showerhead height. I installed a straight new run of pipe for both H&C, rather than tapping into the bath taps etc. I used 15mm and full bore isolators.
Being quite disappointed with the flow rate from the showerhead, I went to check the filters and found that they are part of a NRV. If I blow through the NRV it seems to take a lot of force to open.

Given that I have balanced pressure from each side, can I just remove the NRVs? My understanding is that they are only there to prevent back-syphoning, which I can achieve by using a shorter hose to the showerhead.

 

[longdogs]

Don't tell anyone.

 

[DeeEyeAye]

Done... and the wife still not happy with the flow rate

So what's next? Rip it all out and put in 22mm instead?
Or a pump?

 

[TCCHeating]

Gravity showers are never going to give you a good flow rate. 3m head equals 0.3 bar. 22mm pipe might give you slightly better results at 0.3 bar but I would start looking at shower pumps if i were you. However you may need extra water storage capacity in the loft with a pump so it can become quite costly to install a pump