Packet fragmentation and VPNs

is it normal to see the following when you do a show cry ipsec?
We have two sites connected via l2l tunnel. There are some voice quality issues and it looks like there is packet fragmentation. Could this affect the voice quality? Users are complaining about static and not being able to hear all of the words (they get cut off)

If you define an MTu size and MSS size, could it fix the fragmenetation

#pkts encaps: 4777, #pkts encrypt: 4783, #pkts digest: 4783
      #pkts decaps: 2914, #pkts decrypt: 2914, #pkts verify: 2914
      #pkts compressed: 0, #pkts decompressed: 0
      #pkts not compressed: 4777, #pkts comp failed: 0, #pkts decomp failed: 0
      #pre-frag successes: 6, #pre-frag failures: 0, #fragments created: 12
      #PMTUs sent: 0, #PMTUs rcvd: 0, #decapsulated frgs needing reassembly: 15
      #send errors: 0, #recv errors: 0

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