Oh Annieg what a dilemma, I do not know either of these machines, but I am presuming that the 1015 is a much newer machine than the minimatic - can you find out when these machines were made - that might help with the decision. I suppose as with all things there is a time limit on Bernina actually still stocking spare parts for the older machines, and once that line has dried up then there is not a lot you can do about this. Also I believe that the 1015 is a full sized machine whereas the minimatic is probably smaller - it all depends on your usage, if your need is more for a full sized machine then there is your answer.
Now only recently I had notification from Bernina that they have recently announced that they have some newer feet for the older machines, and then they listed the feet and the models that they would fit - why not go on Bernina's website and see if you can find this, as that may help. The article was sent this last Monday and called 'New Presser Feet for Old Sewing Machines', they then listed a few, and then specifically mentioned the vintage machines of the fifties, sixties and seventies and in particular the 730 and 830 Record, and these feet are height adjustable.