IF, and this is a big IF, you have adequately sized supply and it's limited ONLY by the pressure, then your best solution is a retrofit pump/storage tank. These are available in a pre-engineered package. It isn't all that big, and all you need is a little bit of room near where the water comes into the house and a place to plug it in. You cut the main line, run it into the pump and reconnect the other cut end of the pipe into the outlet of the small storage tank. The pump runs, fills the small tank with pressurized water, and stops. The tank is there so the pump doesn't need to run each time you might want to brush your teeth with a small volume of water. Only when there's an extended use that brings the pressure down by emptying the tank does the pump turn back on (such as filling a tub, taking a shower, or filling the washing machine).
If you search the 'This Olde House' archives, they installed one in a house with this type of a problem, and you can see what's involved. Much easier to see it rather than talking about it.
I thought that the utility is required to provide 'useable' volume AND pressure...15psi isn't, at least for us spoiled AMericans! I've lived in places in the Middle East that used gravity fed storage tanks on the roof that provided about that, but I'd not call them great (but better than carrying water!).