I value IHG points at like 0.8cents (ThePointsGuy has it at 0.7cents, so similar), so the 60000 difference would be like 480.- - 120 = 360, with the 15k offer being worth 120.

If you transfer it to miles, it's still

15k = 3k miles*0.02= 60 dollars
60k = 12k miles*0.02=240.- - 120.- = 120.-

either way, it'll then come down to how much you value a hard pull.