About to fit a new shower,toilet and sink to my daughters en suite and have noticed the hot water supply is in 15mm copper. The hot water comes from a copper hot water cylinder fed from via 28mm pipe from the 140ltr tank in the loft. the 15mm pipe is tee'd into the 22mm hot water pipe that feeds the rest of the house. The pipe run to the en suite is about 9m and the hot water pressure and flow seems ok but I will be changing the taps to a mixer. Should I replace the 15mm pipe with 22mm.