Help higher memory use VPS even in off peak

Hello all! These days I can see my site use higher memory if there's no much traffic. I have a fully managed VPS. When I'm taking following information there's only 8 active visitors on my site. It's off peak time. How do I check this VPS memory eating item? 1536MB Guaranteed RAM 65GB RAID-10 Disk Space 2x Priority 8+ CPUs 3500GB Premium Bandwidth
total used free shared buffers cached Mem: 1572864 634944 937920 0 0 0 -/+ buffers/cache: 634944 937920 Swap: 0 0 0 Total: 1572864 634944 937920
Filesystem Size Used Avail Use% Mounted on /dev/vzfs 65G 17G 49G 25% / /dev/simfs 65G 17G 49G 25% /tmp none 768M 4.0K 768M 1% /dev
[QUOTE]Total processors: 16 Processor #1 Vendor GenuineIntel Name Intel(R) Xeon(R) CPU E5620 @ 2.40GHz Speed 2400.071 MHz Cache 12288 KB Processor #2 Vendor GenuineIntel Name Intel(R) Xeon(R) CPU E5620 @ 2.40GHz Speed 2400.071 MHz Cache 12288 KB Processor #3 Vendor GenuineIntel Name Intel(R) Xeon(R) CPU E5620 @ 2.40GHz Speed 2400.071 MHz Cache 12288 KB Processor #4 Vendor GenuineIntel Name Intel(R) Xeon(R) CPU E5620 @ 2.40GHz Speed 2400.071 MHz Cache 12288 KB Processor #5 Vendor GenuineIntel Name Intel(R) Xeon(R) CPU E5620 @ 2.40GHz Speed 2400.071 MHz Cache 12288 KB Processor #6 Vendor GenuineIntel Name Intel(R) Xeon(R) CPU E5620 @ 2.40GHz Speed 2400.071 MHz Cache 12288 KB Processor #7 Vendor GenuineIntel Name Intel(R) Xeon(R) CPU E5620 @ 2.40GHz Speed 2400.071 MHz Cache 12288 KB Processor #8 Vendor GenuineIntel Name Intel(R) Xeon(R) CPU E5620 @ 2.40GHz Speed 2400.071 MHz Cache 12288 KB Processor #9 Vendor GenuineIntel Name Intel(R) Xeon(R) CPU E5620 @ 2.40GHz Speed 2400.071 MHz Cache 12288 KB Processor #10 Vendor GenuineIntel Name Intel(R) Xeon(R) CPU E5620 @ 2.40GHz Speed 2400.071 MHz Cache 12288 KB Processor #11 Vendor GenuineIntel Name Intel(R) Xeon(R) CPU E5620 @ 2.40GHz Speed 2400.071 MHz Cache 12288 KB Processor #12 Vendor GenuineIntel Name Intel(R) Xeon(R) CPU E5620 @ 2.40GHz Speed 2400.071 MHz Cache 12288 KB Processor #13 Vendor GenuineIntel Name Intel(R) Xeon(R) CPU E5620 @ 2.40GHz Speed 2400.071 MHz Cache 12288 KB Processor #14 Vendor GenuineIntel Name Intel(R) Xeon(R) CPU E5620 @ 2.40GHz Speed 2400.071 MHz Cache 12288 KB Processor #15 Vendor GenuineIntel Name Intel(R) Xeon(R) CPU E5620 @ 2.40GHz Speed 2400.071 MHz Cache 12288 KB Processor #16 Vendor GenuineIntel Name Intel(R) Xeon(R) CPU E5620 @ 2.40GHz Speed 2400.071 MHz Cache 12288 KB