:: These i/p are from sensors which senses
5v D.C.and are directly connected to the i/p.
::

Life could be much easier if you can invert the input from the sensor and get to read a low for an active state.

Out of the 15 I/O pins, you said you have to use 7 for out put and need 10 more for input. So you actually need 2 more in reality.

For the outputs you can use a 3 to 8 decoder like the 74138. You will thus have 3 pins for output and 12 pins for input.

OK this is one way - there are lot many such decoders available.

Raghu