I also tried like this:

<QueryList>
  <Query Id="0" Path="Application">
    <Select Path="Application">
        *[System[(Level=0) and TimeCreated[@SystemTime > '2015-04-14T00:00:00.000000000Z']]]
    </Select>
  </Query>
</QueryList>

This only returns two events and I have about a hundred when I use the Event Viewer regular interface.

The problem does not seem to be related to the query but to a restriction in query mode.