Without any hint where the performance degradation is this is hard to tell. Overall, over time, performance on specific programs may drop a few percent (say < 10), while others may get much faster. Anything else is a bug. I do not recall changes that should explain more than tiny slowdowns. It depends a little on the versions though. Changes to stack growing/GC scheduling have caused problems and the same is true for scheduling clause GC. Both are fixed (well, on the programs they showed up). I’d give 8.1.13 a try. I think practically the only incompatibility is a more uniform and stricter implementation of the command line arguments.
Otherwise, comparing a profile/1 run is the easiest way to get a clue.