Vishwa, until PHP 5.x, 64-bit support for Windows platform though was available, but limited (no large integer support), since PHP 7.x, 64-bit version for windows are fully supported (see attachment below from Window's PHP page), so feel free upgrading PHP, in fact you should have done it as soon as moodle support for PHP 7.x was initiated (since version 3.0.1)
Just make sure your Moodle supports PHP 7.1, as being latest, I think its since Moodle 3.4 PHP 7.1 is supported, else go for PHP 7.0.X
