When creating a backup, UpdraftPlus uses Binary Zip or PHPZip to compress the backup files. If neither Binary Zip or PHPZip are available on your server, UpdraftPlus will use PclZip. PclZip is older and slower than Binary Zip or PHPZip and this may be causing your backups to slow down. Please ensure the PHPZip module is turned on. You can action this directly via cPanel or by contacting your web host for support.