Sometime around 1971 BMC/Leyland in their wisdom changed the engine prefix numbers to "reduce the number of stamping operations, a simplified??? Serial Number prefix code for Australian power units is released". Quote from Clubman parts manual December 1972-PUB 1052.
It only has codes for Mini 1100, Mini 1100 Van, Mini Clubman and Clubman GT.
1100 Mini and van and 1100 Clubman codes became 10 +00 to 05 depending on model and if high or low compression ( was 10Y) and Clubman GT became 1200 (was 9FXEY). 1201 was a replacement short engine for Clubman GT.
Clubman GT cars with the non Cooper 'S' engine used 1206. (Not in parts book but from Gavin's NZ site)
Don't have any info for Mini K but the later cars would have been caught up in the number changes so 1015 could be a Mini K.
Regards
RonR