I dont like the 'its only £15' patter, I really dont. £15 to one person is heehaw, but to the next can be a sum of money that they cant do without...
...that said, the Club is a business as Joeboy pointed out, and I'm pretty sure they wouldnt have just plucked these figures out of thin air, they will know roughly how many they will sell and what sort of money that need to charge. If you dont want to buy because of the increase and believe its not worth it in comparison to the gate price and/or potentially missing games, or you genuinely cant afford the increase then fair-do's but get over it. The Club are in a financial position where they need to squeeze as much money as they can out of their fans, either pay it or dont.
For what its worth, I buy mine because if I dont it may well break the habit of me going at all, its also a shared interest for me and my boys (though they dont even sit with me these days) and something for us to do on a Saturday afternoon...its also a relatively inexpensive few hours out the house.