If these crashes started before you upgraded to OS X 10.11 and or you installed LR 2015.2.1 then it is a hardware problem. More than likely a RAM problem.
"IF" you never had LR installed before and this is a New Mac that came with OS X 10.11 there are some serious bugs in the most current release of LR that are causing all kinds of problems on OS X 10.x. So much so Adobe originally release 2015.2 then just 4 days later released 2015.2.1 to correct Some of the problems but not all.