Continuous heavy memory allocations

Started MC tonight and it auto-updated from 1.9.2 to 1.9.4, started playing on a single-player instance created last week under 1.9.2, and all was fine. Suddenly, after about my tenth death, began experiencing bad stuttering. F3 showed that memory usage was going from 33% (of 2 GB Java min/max) up to 88% within about 15 seconds (about 1 GB in 15 seconds), at which point a GC would take place (causing a half-second pause) going back to 33% usage and then the cycle would repeat, continuously. Cannot get out of this unusable state.