Slow pptp connection on mikrotik router

Hi,

I just installed a new mikrotik router RB951G-2HND. and running the latest software of the os.

The mikrotik is connected directly to my cable modem. Connected behind the microtik I have a ddwrt router with a pptp connection to a pptp server. I used to get 15mb/3mb now when I switched to the microtik to as my main router, I get speeds of 3mb/1mb.

If I connect to the microtik directly with my laptop I get 15/3 speeds, yet if I engage a pptp connection (via software not the ddwrt router) from the laptop my speed goes down to 3/1mps !

Can anyone help me… im a noob!

Thanks