I didn’t even read the whole OP... too long, just picked up on others responses
You can’t get more out of less (apart from more aggro out of a less than perfect installation ).
If you have “15lpm” coming into your property, that is all you have and will be subdivided by each outlet/demand that is imposed upon it.
You need to calculate your own flow-rate, within your boundary using a container of known volume and a stopwatch, you can then do some simple math to calculate what litres-per-minute you are getting.
This needs to be done from the least restricted outlet that you can access - typically an outside tap or washing machine valve... kitchen taps are often restricted by flexi-hoses and internal gubbins to shape spray pattern etc.
Once this figure has been obtained you can then ask your water supplier to carry out a similar test at their stopcock, to your property. This will show if it is worth upgrading your main from the street to your internal stopcock.