Your local server likely doesn't have the simple XML functions enabled.. don't change the script.. update the PHP enabling the needed features.
You can use check-fetch-times.php?show=info on your site to show if the needed functionality in PHP is enabled. A working version would look like this
check-fetch-times.php Version 1.21 - 28-Feb-2018
Website PHP information
Webserver OS: Linux s19486853.onlinehome-server.com 2.6.32-042stab127.2 #1 SMP Thu Jan 4 16:41:44 MSK 2018 x86_64
PHP Version: 7.2.3
Document root: /var/www/vhosts/s19486853.onlinehome-server.com/httpdocs/wx
allow_url_fopen = ON
allow_url_include = off
Stream support for http is available
Stream support for https is available
Streams supported: compress.bzip2, compress.zlib, data, file, ftp, ftps, glob, http, https, phar, php, zip
Status of needed built-in PHP functions
function simplexml_load_file is available
function iconv is available
function json_decode is available
function curl_init is available
function curl_setopt is available
function curl_exec is available
function curl_error is available
function curl_close is available
function curl_getinfo is available
function imagecreatefrompng is available
function imagecreatefromjpeg is available
function imagecreatefromgif is available
class Imagick is available (but is not required/used by the Saratoga templates)
Current required cURL features status:
cURL version: 7.19.7
cURL SSL version: NSS/3.27.1
cURL libz version: 1.2.3
SSL is available
LIBZ is available
cURL protocols supported: dict, file, ftp, ftps, http, https, ldap, ldaps, scp, sftp, telnet, tftp
Current GD (image handling functions) status:
GD support: is available.
GD Version: bundled (2.1.0 compatible)
FreeType Support: is available
FreeType Linkage: with freetype
GIF Read Support: is available
GIF Create Support: is available
JPEG Support: is available
PNG Support: is available
WBMP Support: is available
XPM Support: is available
XBM Support: is available
WebP Support: is NOT available
BMP Support: is available
JIS-mapped Japanese Font Support: is NOT available
If any in the first part are marked as 'NOT available', that's a PHP setup issue you'll need to resolve. In the GD set, only GIF, JPEG and PNG are needed.. the others are optional (and not used by the Saratoga templates).