{{--------------- S Y S T E M ---------------

OS:PRETTY_NAME="Raspbian GNU/Linux 8 (jessie)"
NAME="Raspbian GNU/Linux"
VERSION_ID="8"
VERSION="8 (jessie)"
ID=raspbian
ID_LIKE=debian
HOME_URL="http://www.raspbian.org/"
SUPPORT_URL="http://www.raspbian.org/RaspbianForums"
BUG_REPORT_URL="http://www.raspbian.org/RaspbianBugs"

uname:Linux 4.1.7-v7+ #817 SMP PREEMPT Sat Sep 19 15:32:00 BST 2015 armv7l
libc:glibc 2.19 NPTL 2.19
rlimit: STACK 8192k, CORE 0k, NPROC 7720, NOFILE 65536, AS infinity
load average:6.96 6.49 5.16

/proc/meminfo:
MemTotal: 996840 kB
MemFree: 42220 kB
MemAvailable: 403188 kB
Buffers: 68460 kB
Cached: 316472 kB
SwapCached: 0 kB
Active: 782744 kB
Inactive: 130488 kB
Active(anon): 529420 kB
Inactive(anon): 9168 kB
Active(file): 253324 kB
Inactive(file): 121320 kB
Unevictable: 0 kB
Mlocked: 0 kB
SwapTotal: 102396 kB
SwapFree: 102396 kB
Dirty: 108 kB
Writeback: 0 kB
AnonPages: 528324 kB
Mapped: 74620 kB
Shmem: 10264 kB
Slab: 25312 kB
SReclaimable: 13604 kB
SUnreclaim: 11708 kB
KernelStack: 1640 kB
PageTables: 3892 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
WritebackTmp: 0 kB
CommitLimit: 600816 kB
Committed_AS: 1069508 kB
VmallocTotal: 1056768 kB
VmallocUsed: 4772 kB
VmallocChunk: 827404 kB
CmaTotal: 8192 kB
CmaFree: 3588 kB

CPU:total 4 (ARMv7), vfp

/proc/cpuinfo:
processor : 0
model name : ARMv7 Processor rev 5 (v7l)
BogoMIPS : 64.00
Features : half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm
CPU implementer : 0x41
CPU architecture: 7
CPU variant : 0x0
CPU part : 0xc07
CPU revision : 5

processor : 1
model name : ARMv7 Processor rev 5 (v7l)
BogoMIPS : 64.00
Features : half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm
CPU implementer : 0x41
CPU architecture: 7
CPU variant : 0x0
CPU part : 0xc07
CPU revision : 5

processor : 2
model name : ARMv7 Processor rev 5 (v7l)
BogoMIPS : 64.00
Features : half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm
CPU implementer : 0x41
CPU architecture: 7
CPU variant : 0x0
CPU part : 0xc07
CPU revision : 5

processor : 3
model name : ARMv7 Processor rev 5 (v7l)
BogoMIPS : 64.00
Features : half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm
CPU implementer : 0x41
CPU architecture: 7
CPU variant : 0x0
CPU part : 0xc07
CPU revision : 5

Hardware : BCM2709
Revision : a01041
Serial : 0000000094661c92

Memory: 4k page, physical 996840k(42220k free), swap 102396k(102396k free)

vm_info: Java HotSpot(TM) Client VM (25.0-b70) for linux-arm-vfp-hflt JRE (1.8.0-b132), built on Mar 4 2014 06:39:31 by "java_re" with gcc 4.7.2 20120910 (prerelease)
}}

World Gen is really slow specially on an underpowered device, pre-gen your world

It's possible you ran out of resources considering you're running it on a Pi.