Vertical radiator instead 2 old

[Donnpass]

Hi all, i have removed 2x old radiators in my extension and there i want to put big one 6500/7000 btu vertical aluminium rad, does my 10mm pipe work fine on it ? Also I will need to extend pipe araund 6m one way and same return is this should be enough? or i can just do this 6m with 15mm pipe extension ? Thank you