Yes you can. Just make sure you assign each keypad its own address (ex. 6160 set to address 16, 1st 6150 address 17, 2nd 6150 address 18). You can get 6160's at a fairly reasonable price on eBay, why not just use all 6160's? I'm not a fan of the fixed display keypads like the 6150's.
These are basic questions that you should know that answer to if you're installing this system. I suggest you fully read over the programming guide and installation manual before you install it.
How many devices are you going to install on this system and will it include fire and CO? Also, are you going to be using wireless sensors?
Let us know if you need any additional help.