Depends on the pedals. Most will take a 15 mm open wrench, and it may need to be thinner than a normal wrench or adjustable. Pedal wrenches are generally very long because pedals can get very tight. Go ahead and see if your adjustable wrench will fit the pedals, and if so, give it a try. Remember that the left pedal has left-hand threads. If you can't get them off even though your adjustable wrench fits, then you need the extra length of real pedal wrench.
Oil is good, grease is better.
2007 Peter Mooney w/S&S couplers/Terry Butterfly
1993 Bridgestone MB-3/Avocet O2 Air 40W
1980 Columbus Frame with 1970 Campy parts
1954 Raleigh 3-speed/Brooks B72