Do these pipe sizes look reasonable?

I'm moving from a warm air system to a wet one and have the sizes of
radiators required for each of the rooms (quote from plumbing co). I'm
planning 22mm from the boiler teeing off to 15mm feeds for the front &
back downstairs.

front 5.9kw (2.1+2.8+1)
back 3.1kw (1+2.1)

For the upstairs teeing off the 22mm from the boiler with 15mm.
front 3kw (1.4+1.6)
back 2kw (1.3+0.7)

As you can see then it's 15mm to all the rads. Could there be a problem
with sludge (low water speed) to the 0.7kw radiator in particular, or
have I confused myself with all the Googling I've been doing, concerning
10mm pipe! I'm doing it all in plastic (except the boiler - Worcester
Bosch 30cdi probably).
Thanks
Gary

As you can see then it's 15mm to all the rads. Could there be a problem
with sludge (low water speed) to the 0.7kw radiator in particular, or
have I confused myself with all the Googling I've been doing, concerning
10mm pipe! I'm doing it all in plastic (except the boiler - Worcester
Bosch 30cdi probably).

It'll be fine. Just make sure you use inhibitor. Also consider running the
pipework so that the heating can be easily subzoned. This way, you can run
the downstairs heating at different times to the upstairs heating, which
saves you money and is better for the environment.

Christian.