Thanks CJ for that.Hi there, EngHK - and welcome to the forum!
To answer your question - you can't use a 15kg reel on it.
If i'm thinking of the right welder, I've seen a few yellow cosmo's in the past, and they appear to be the same as the grey SIP MigMate, and they'll only take a 5kg spool of wire.
All the Best,
CJ
You can make a frame to hold the 25kg spool and feed the wire to the welder through a curtain wire