I am refurbishing my utility, and want to bury some exposed 15 mm pipes in
the concrete floor.

I'd use PEX, rather than copper, my feeling is that they're less likely to
leak. Also, it is better to not actually bury, but leave a trench and board
over the trench, so that if the pipes need servicing, it is just a case of
lifting the lino and undoing screws, rather than getting the jack hammer out
and demolishing the floor and what is left of the pipes. I'd still use PEX
in the trench, too.

Christian.