pruning old roses?

Having recently aquired this garden, the roses are about 15 years old can I prune down to 12" each main stem.?

 

Hi, have you looked at the stems, how many living buds they have? Are they climbers, ramblers, teas or shrubs? Each category needs different treatment... Anyway, 12" sounds far too drastic for me for such old bushes, no matter what sort they are.

I'd dare prune them only very slightly in the first spring, cutting back the stems only halfway - or even less - and see how they tolerate it. You cannot guess how they had been treated before and how they'll respond to regular pruning... And until next spring, I'd try to identify all to see what should be done to each bush. Or, at least, that's what I'd do.