One privvmpage unit is 4 kb of memory. Here's the entire container config, see if it helps
amber:/etc/vz/conf# cat 107215.conf
# PVE default config for 256MB RAM
ONBOOT="no"
# Primary parameters
NUMPROC="1024:1024"
NUMTCPSOCK="9223372036854775807:9223372036854775807"
NUMOTHERSOCK="9223372036854775807:9223372036854775807"
VMGUARPAGES="1310720:9223372036854775807"
# Secondary parameters
KMEMSIZE="9223372036854775807:9223372036854775807"
OOMGUARPAGES="1310720:9223372036854775807"
PRIVVMPAGES="15728640:16777216"
TCPSNDBUF="9223372036854775807:9223372036854775807"
TCPRCVBUF="9223372036854775807:9223372036854775807"
OTHERSOCKBUF="9223372036854775807:9223372036854775807"
DGRAMRCVBUF="9223372036854775807:9223372036854775807"
# Auxiliary parameters
NUMFILE="9223372036854775807:9223372036854775807"
NUMFLOCK="9223372036854775807:9223372036854775807"
NUMPTY="255:255"
NUMSIGINFO="1024:1024"
DCACHESIZE="9223372036854775807:9223372036854775807"
LOCKEDPAGES="655360:655360"
SHMPAGES="9223372036854775807:9223372036854775807"
NUMIPTENT="9223372036854775807:9223372036854775807"
PHYSPAGES="0:9223372036854775807"
# Disk quota parameters
DISKSPACE="67108864:73819750"
DISKINODES="12800000:14080000"
QUOTATIME="0"
QUOTAUGIDLIMIT="0"
# CPU fair sheduler parameter
CPUUNITS="1000"
CPUS="1"
VE_ROOT="/var/lib/vz/root/$VEID"
VE_PRIVATE="/var/lib/vz/private/$VEID"
OSTEMPLATE="centos-5-standard_5.4_amd64"
ORIGIN_SAMPLE="pve.auto"
IP_ADDRESS="192.168.107.215"
HOSTNAME="mail.domain.com"
NAMESERVER="192.168.102.5 192.168.101.112"
SEARCHDOMAIN="domain.com"