XSLT select by child node value

I am trying to process an XML file with XSLT, where I need to select nodes by child value. I tried to simple filter out results by regex, but maybe it is not the most elegant way to do this. I think XSLT is an universal solution to do this transform, if not please suggest me a better solution. The XML file actually look like this:

<?xml version="1.0" encoding="windows-1250"?>
<SHOP>
<SHOPITEM>
<unknown_element1></unknown_element1>
<unknown_element2></unknown_element3>
...
<YEAR>2015</YEAR>
<unknown_elementxy><unknown_elementxy>
...
</SHOPITEM>
<SHOPITEM>
<unknown_element1></unknown_element1>
<unknown_element2></unknown_element3>
...
<YEAR>2014</YEAR>
<unknown_elementxy><unknown_elementxy>
...
</SHOPITEM>
<SHOPITEM>
<unknown_element1></unknown_element1>
<unknown_element2></unknown_element3>
...
<YEAR>2015</YEAR>
<unknown_elementxy><unknown_elementxy>
...
</SHOPITEM>
</SHOP>

I want to keep current XML structure, but keep only nodes where = 2015. The desidered output:

<?xml version="1.0" encoding="windows-1250"?>
<SHOP>
<SHOPITEM>
<unknown_element1></unknown_element1>
<unknown_element2></unknown_element3>
...
<YEAR>2015</YEAR>
<unknown_elementxy><unknown_elementxy>
...
</SHOPITEM>
<SHOPITEM>
<unknown_element1></unknown_element1>
<unknown_element2></unknown_element3>
...
<YEAR>2015</YEAR>
<unknown_elementxy><unknown_elementxy>
...
</SHOPITEM>
</SHOP>

<unknown_element> = there are many different elements in the node, the XSLT should keep current structure of the actual node. Just need to filter out nodes by .