I have the Mac version of the game and have made it to mission 18. Needless to say my attempts even on easy have been unsuccessful. I even tried to use the cheats to complete all the missions so I could play the next mission but I can not get them to work on my Mac version.

I have breached the castle on the "west" wall many times but I never have enough troops to get to the pig. Any advice on how to get past this mission would be appreciated so I can fight the Wolf. Thank you.

HI! Best way to win this mission is moving with archers a little bit forward to reach max range, then shoot until all units are dead. Like here:

http://www.youtube.com/watch?v=msEvqSx3nAo

This mission basically cannot be won with any conventional tactics; you have to be punk-ass cheap and snipe off the Pig's archers from vantage points where they can't shoot back. Use the hills and ridges in front of the Pig's castle to find some of these "sweet spots" that let you do this. You'll probably need to save scum, save after you kill any of the Pig's archers or crossbows, and load if he successfully kills any of your's. You're so out-gunned on the archery-department that you basically cannot afford any casualties until your final push. Once you've cleared off the front wall, you can roll up the ram and break open the gates, then roll the siege tower in to the second layer of walls and storm them. It's all pretty straightforward from there (just be mindful of the Pig's pitch traps).

I found this video walkthrough by RazingHel quite useful: https://www.youtube.com/watch?v=FD77iLwWp2c

I actually think this mission was easier than 15, if only because of the absence of a time limit. I tried to use my archers and crossbowmen to attack the Pig's units on the walls, but after letting the game run for a long time at speed 90, they only managed to kill two. So I followed the approach on the video, first provoking the Pig with some spearmen so he'd light the pitch ditches, then filling the moat in the southwestern side. Instead of using the ram to break the walls I used two tunnelers (screenshot 1). I prefer tunnelers to the ram, and if you select the appropriate distance, they can start digging the tunnel at a place which is out of range from the enemy.

After that, sending a siege tower (with some infantry units at the same time to distract the enemy archers and crossbowmen) and getting it to the inner walls is the key (screenshot 2). Once the siege tower is in position, throw units onto the walls, focus on killing the units on the towers on the western side, wait until the Pig ignites the pitch ditches in the inner courtyard, and after that go straight to the keep to slaughter him. You can ignore the rest of units of the castle (screenshot 3).

Happy banquet!

How did you beat mission 15? I'm having a lot of trouble with that one. Frontal assault? Everyone dies. Snipe everything? Too long, because the arrows just bounce off the walls. Try to use ladders? Units go full retard and either stand still and wander around aimlessly. Try to dig a moat? Ditto.

I did manage to clear the front court yard one time, but I only had like 8 crossbow men and 2 archers, and for some reason their arrows kept missing the last few garrisons.

What a terribly designed level, how did this get past play testing.

You've got some suggestions and strategies for level 15 here:
https://www.gog.com/forum/stronghold_series/hope_this_helps_stronghold_hd_lvl_15_carving_a_path_on_hard

I already did it. Those tricks didn't work, as they took too long and required too much micro.
I did find one that was a bit easier to pull off, but I noticed it still depends on luck, as there's a good chance you'll lose all of your soldiers in the initial assault anyway.

I had to sacrifice my ram and ladders to take the heat off of my melee and archers. The good news though that if enough macemen survive, they can go around killing the archers pretty easily. Well, until the AI goes full retard and makes them wander away when they are supposed to be going to a tower.

That's too frequent for the AI. I find filling the moat particularly infuriating; unless you constantly redirect your units to work in a specific zone, they will spread out around all the walls, turning them into easy targets without actually finishing the job.

Yeah, I had that problem too. They just wander off and start digging a part of the moat that's nowhere near where you want it. I found reducing the game speed to 10 helps, as it gives you time to order them to behave.