Hi,
Page load depends on how many packages your loading in a page. If you load too many packages in a single page it will take more time and it totally depends on your server performance.
In a normal page WPDM does not apply much load. And in our latest version we actually optimized performance. So WPDM works better than ever before.
However to monitor this issue closely i need to check your installation. If you want that, please send temporary wp-admin login info in private reply.
Thanks.