Custom Sort apps script (pulling data from 12 sheets) is slow

Question

I have a code that someone wrote for me to make import data easier instead of having to write a formula that pulls data from 12 sheets (and is open to error). The script has a sheet of "links" along with sheet names and ranges. It works fine when I use the "menu" that it created for importing the data, but it is slow (I'm guessing because it is going through 12 sheets). If i need to link the spreadsheet, please let me know.

function onOpen(e) {
  SpreadsheetApp.getUi().createMenu('IMPORT')
    .addItem('Update data', 'customImport')
    .addToUi();
}

function customImport() {
  const ss = SpreadsheetApp.getActiveSpreadsheet();
  const inputSheet = ss.getSheetByName('Sheet16');
  const outputSheet = ss.getSheetByName('Sheet17');
  const columnNumberToFilter = 1

  const inputValues = inputSheet.getRange(2, 1, inputSheet.getLastRow() - 1, 3).getValues();
  const output = [];

  inputValues.forEach(entrie => {
    const [url, sheetname, range] = entrie;
    const sheetRange = SpreadsheetApp.openByUrl(url)
      .getSheetByName(sheetname)
      .getRange(range)
    const data = sheetRange.getValues();
    data.forEach(row => {
      if (row[columnNumberToFilter - 1] != "") {
        output.push(row)
      }
    })
  })

outputSheet.getRange(4,1,outputSheet.getLastRow(), outputSheet.getLastColumn()).clearContent();
outputSheet.getRange(4, 1, output.length, output[0].length).setValues(output).sort([4,5]
)
}