No, you just didn't read the "What's New" information that would have explained the Write to Spreadsheet File has been replaced with Write Delimited Spreadsheet, which is largely the same Function + the Error Wire.
I have just installed labview 2015 platform. But “write to spreadsheet file” is not present.
Of course the old version is also still present, but show a red x across it to tell you that it is obsolete. The old version still works exactly as before but is no longer accessible from the palettes.
All old code will continue to function without any need to replace anything.