Worth increasing pipe sizes

I'm running pipes to location for a new combi. The flow and return are 22, so ill run them in 22. The DHW and cold inlet are both 15 at boiler. Would there be any benefit in running up to the boiler in 22 then reducing to 15 at boiler? Or just run it in 15 all the way to the boiler.

 

15 mm ,copper. No point in using 22mm for cold feed and DHW.

 

Understood. But it will be PEX to within a meter or so. Does that alter your opinion?

 

Do it all in copper ,soldered fittings, don't bury it in concrete ,then forget about it all for around 50 years !
That's my opinion ,for what it's worth.

 

If doing it in plastic, might be worth going for 22mm as the plastic fittings are rather restrictive