Actually, WP Travel Pro plugin is the bundle of all the modules and features. So, when we activate WP Travel Pro plugin all the features and modules will be activated which is the reason for the slow speed (website running slow).
So, please disable the modules which are not required for you by going to Admin Panel > WP Travel > Settings > Modules Settings > Pro Modules as shown in the screenshot given below.
Also, please disable unused payment gateways by going to Admin Panel > WP Travel > Settings > Modules Settings > Payment Modules as shown in the screenshot below.
Further, if you have any queries, please submit them to our Contact page.